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Fingerprint Scanning and Comparison

Using the Document Reader SDK with the compatible devices, you have the ability to scan and compare the finger images from different sources: from the document's RFID chip and the fingerprint scanner.

The current page describes how to set up and perform the fingerprint scanning procedure.


ID Document

  • ID document with RFID chip, containing fingerprints data


  • Compatible fingerprint scanner from one of the manufacturers:
  • Regula or third-party compatible Document Reader device with integrated RFID scanner module.


Use the custom Document Reader SDK installation procedure with the third-party modules option selected. This step ensures the installation of all needed additional libraries. See the screenshots below.

Document Reader SDK Installation Wizard window demonstrating selected custom installation option

Document Reader SDK Installation Wizard window demonstrating selected third-party modules option

Before You Start

1. Connect both the Document Reader and the Fingerprint Scanner devices to the PC.

2. Launch the Document Reader (READERDEMO.EXE) desktop application.

3. Open Options dialog window (from the main toolbar panel, or from the File menu, or press Alt + F8).

Document Reader Test Application with Options dialog window, opened on the General tab and highlighted Fingerprints sections

4. Use the subsections Fingerprints scanning and Fingerprints comparison to define the parameters related to fingerprint processing.

See the table with configuration parameters and their descriptions below.

Fingerprint scanning

Parameter Values Default Description
Auto scan fingerprint on/off on Whether to automatically open the UI form after the document scanning and processing is finished.
Graphic format for fingerprints .jpg
.jpg Graphic format of the image, in which the fingerprint is processed and saved.
Fingerprint scan library BiolinkFPR.dll
Software library used for fingerprint scanning. The concrete selection depends on the fingerprint scanner vendor.
Quality 0-100, % 60 Minimum acceptable quality of the fingerprint image in percent. The device continues repetitive scanning until the quality of the resulting fingerprint image reaches or exceeds the defined value.
Timeout any integer, ms 5000 The timeout for fingerprint scanning in ms. If the resulting fingerprint image quality doesn't reach the defined quality percent during the specified time interval,the scanning process stops.

Fingerprint comparison

Parameter Values Default Description
Fingerprint compare library RegulaFPR.dll
Software library used for fingerprint comparison. If not selected, the fingerprints are only scanned, but not compared with the data, extracted from RFID chip.
Threshold 0-2000 600 Minimum acceptable threshold for the fingerprint comparison result. For most cases, the concrete value is selected empirically. For example, the default 600 value corresponds to approximately 97% of compared fingerprints coincidence.

5. For the document scanning device to obtain the fingerprint data from the document, go to the RFID Chip tab of the same Options dialog window and select the parameters as displayed below.

Document Reader Test Application with Options dialog window, opened on the RFID chip tab and highlighted Fingerprints data groups

As shown in the picture, select the following data groups:

  • Biometry - Fingerprint(s) (DG3) in RFID ePassport data groups section
  • Biometry - Fingerprint(s) (DG7) in RFID eDL data groups section

Now, during the document scanning process, the specified data fields will be extracted from the RFID chip.

6. Define where and in what format the results of document scanning and fingerprint comparison will be saved. Go to the Results tab of the Options dialog window and select the appropriate parameters.

Document Reader Test Application with Options dialog window, opened on the Results tab and highlighted results saving variants

As you can see in the preceding image, the results can be saved in the formats:

  • TXT
  • PDF
  • XML
  • JSON

You can also select the custom folder, where these files will be saved.

Note that due to security reasons, the actual fingerprint images are not saved to the PC anyway, only the comparison results in statistical form are stored.

Processing in Test App

After performing all the preliminary steps, you can process the fingerprints. Follow the instructions further.

1. Using the document reader device, scan the ID document with RFID chip, containing the fingerprints' data.

If the data is successfully extracted from the RFID chip and the Auto scan fingerprint parameter is selected in Fingerprint scanning options, the specific UI form is displayed.

Fingerprint scanning and comparison UI form displaying fingerprint data, extracted from the document's RFID chip

The Fingerprint scanning and comparison UI form shows the Reference image from the document's RFID chip in the left-side panel. There is also the dropdown list displayed at the top for the selection of the concrete reference finger image.

Note that the fingers, for which the images have been detected in the RFID chip, are marked with the special fingerprint symbol, see the screenshot:

Fingerprint scanning and comparison UI form displaying the fingers, for which the fingerprints are detected in RFID chip

Now you can proceed with fingerprint scanning and comparison.

2. Using the fingerprint scanner device, scan the finger(s).

The scanning process is either started automatically at the finger(s) detection, or by clicking the corresponding Scan fingerprint button in the Fingerprint scanning and comparison UI form.

After the finger(s) has been successfully scanned, the same UI form is refreshed, reflecting the comparison results for the Reference image and the Real image, recently obtained from the fingerprint scanner device.

Fingerprint scanning and comparison UI form with fingerprint image, extracted from the document's RFID chip, compared with the fingerprint, scanned by fingerprint scanner device

Using the dropdown at the top, you can change the reference finger image. If the selected finger has already been scanned, the corresponding comparison result will be displayed without the need of rescanning.

Also, some methods are available for fingerprints processing via the COM Interface. See the following section for details.

Processing via COM Interface

Besides providing the GUI for controlling the functionality, Test Application also acts as the COM automation server.

By calling methods of the single RegulaReader.READERDEMO COM object, you can operate with different SDK functionality, including fingerprint processing.

All the fingerprint-related COM methods' names start with the FP prefix. See the details and descriptions further.


The FPScan method starts the manual scanning of the finger(s). In scope of the current method you can define only the finger(s) to be scanned, other parameters are taken from the Test Application.


The method takes as a parameter the integer index of the finger to be scanned AFingerIndex.

The value must be selected from the range of constants as follows:

Constant name Value Description
gf_Finger_LeftThumb 300 left thumb
gf_Finger_LeftIndex 301 left index finger
gf_Finger_LeftMiddle 302 left middle finger
gf_Finger_LeftRing 303 left ring finger
gf_Finger_LeftLittle 304 left little finger
gf_Finger_RightThumb 305 right thumb
gf_Finger_RightIndex 306 right index finger
gf_Finger_RightMiddle 307 right middle finger
gf_Finger_RightRing 308 right ring finger
gf_Finger_RightLittle 309 right little finger
gf_Finger_Right4Fingers 313 4-finger image of right hand
gf_Finger_Left4Fingers 314 4-finger image of left hand
gf_Finger_2Thumbs 315 2-thumb fingerprint

Return value

The method returns boolean value, indicating whether the scanning succeeded or not.


The FPScanUI method simply displays the Fingerprint scanning and comparison UI form for you to perform all further actions there.

The method doesn't take parameters or return any value.


The FPScanWithParams method performs the fingerprint(s) scanning in accordance with the given parameters.


The method takes the JSON string with parameters in a custom format, depending on the concrete fingerprint scanner manufacturer.

Below, you can see the example JSON for the Jenetric device.

Example JSON for Jenetric fingerprint scanner (click to expand)
   "finderIndex" : 301,
   "mode" : 3,
   "missinfFingers": 4,
   "contentAnalysesToDisable" : 14

Return value

The method returns boolean value, indicating whether the scanning succeeded or not.


The FPCompare starts the manual comparing of all the fingerprints currently available in the context of the COM object.

That means, to perform the successful fingerprint comparison you need to:

  • Scan the document with RFID chip, containing fingerprint data (to get the reference image)
  • Scan the fingerprint (to get the real image)

If there are multiple fingerprints available for comparison, the SDK subsequently iterates over each reference-real image pair to find any available coincidence.

Return value

The method returns integer value from the eCheckResult enumeration, indicating the status of the completed comparison. See the details below.

Constant name Value Description
ch_Check_Error 0 Fingerprint comparison has been completed with an error
ch_Check_OK 1 Fingerprint comparison has been completed successfully
ch_Check_WasNotDone 2 Fingerprint comparison has not been completed

Results Exploration

After the fingerprint check has been successfully performed, the result of the comparison in the Test Application is demonstrated by the corresponding Fingerprint indicator in the Results panel:

Fingerprint indicator in the Results panel

The detailed comparison result can be obtained either in XML, TXT, PDF, or JSON format (if the corresponding setting is specified in the Options dialog, Results tab).

Additionally, the comparison results are also obtainable from the RegulaReader.READERDEMO COM object, by calling the CheckReaderResult method with eRPRM_ResultType.RPRM_ResultType_FingerPrints result type as a parameter. In this case, the RPRM_ResultType_FingerPrint_Comparison fingerprint comparison results contain the concrete similarity values in percent.

Next Steps