This is an Arduino library for most of the FPMxx/R30x/ZFMxx/R551 optical fingerprint sensors.
(See note below.)

Included is a Python 3 script for extracting fingerprint images to a PC; the image_to_pc example must first be uploaded to the Arduino.
For optimal reliability, baud rates <= 57600 are recommended regarding SoftwareSerial usage, especially when retrieving fingerprint images.

A generic list of commands for these sensors can be found here. Keep in mind that not all sensors (few, really) support all commands. You'll just have to try them out for yourself.
To match templates on your PC/server, check here.
A device-agnostic version of this library in C.
An Arduino library for the GT511C3 (and similar GT5x) fingerprint sensors.

Note:

• The R308 is tentatively supported for now. Since its settings cannot be read by the usual commands, they have to be
  set manually to defaults based on the datasheet, at the risk that these defaults may be wrong. In any case,
  make sure to check the setup() of the R308_search_database example for how to properly initialize your sensor.

• The R551 seems to have several clones, and a datasheet/SDK that's inconsistent with the sensor's actual behaviour.
  To use one of these sensors, make sure to uncomment FPM_R551_MODULE in FPM.h. However, they generally have trouble working with this library, specifically more advanced functionality like image/template downloads.
  To take full advantage of the available functionality, it's recommended you get an FPM10, R305/7 or ZFM60,
  especially the first which has been well-tested with this library.

• If you have an ESP32, you can use this to setup a HardwareSerial port:

#include <HardwareSerial.h>
#include <FPM.h>

/* select UART1 */
HardwareSerial fserial(1);

FPM finger(&fserial);
FPM_System_Params params;

void setup(void) {
    Serial.begin(9600);
    
    /* RX = IO16, TX = IO17 */
    fserial.begin(57600, SERIAL_8N1, 16, 17);
    
    /* the rest of the code follows, same as in the examples */
    if (finger.begin()) {
        ...
    }
}

void loop(void) {
    ...
}