What DPI Do I Need to Scan a Fingerprint Card?

The resolution dropdown on a scanner has a dozen options and most of them are wrong for a fingerprint card. The right answer is 600 DPI, grayscale, saved as PNG or TIFF. This guide explains where that number comes from and the scanner settings worth setting once and never thinking about again.

The short answer

For an FD-258 card destined for an EFT file:

• Resolution: 600 DPI
• Color mode: Grayscale
• File format: PNG or TIFF
• Area: the entire card with a small margin

Every consumer flatbed sold in the last fifteen years supports these settings.

Why 500 PPI - and why 600 DPI is our recommendation

500 PPI is the resolution at which fingerprint images are exchanged in the biometric community. Two sources anchor it:

• The ANSI/NIST-ITL 1-2011 standard - the NIST-published data format for exchanging fingerprints, faces, and other biometrics - defines the minimum scanning resolution for fingerprint images as 19.69 pixels per millimeter ±0.20 ppmm, or 500 PPI ±5 PPI.
• The FBI Electronic Biometric Transmission Specification (EBTS) - the document the ATF eForms system expects submitted files to conform to - references the same resolution floor.

The standard exists because fingerprint matching isn't a pixel-by-pixel comparison. The FBI's pipeline extracts minutiae - the ridge endings and bifurcations that identify a print - and 500 PPI is the resolution at which those features resolve cleanly. NIST's NFIQ 2 fingerprint image quality algorithm is calibrated to 500 PPI for the same reason. As NISTIR 8382 states: "NFIQ 2 is developed for images captured at 500 dpi and as such it shall not be used for images of different resolution."

We recommend 600 DPI rather than exactly 500 for one practical reason: consumer scanners drift. A flatbed set to "500 DPI" produces an image whose effective resolution is close to but not exactly 500 PPI, depending on sensor calibration and how the card sat on the glass. 600 DPI clears the 500 PPI floor with margin, produces a reasonably sized file (~20–40 MB as PNG for a full card), and is available on every consumer scanner.

While scanning at 1200 DPI produces a higher resolution image, it will not increase your NFIQ score or make the fingerprint card materially better for matching. Since the FBI's matching system and the NFIQ algorithm are calibrated around a 500 PPI target, the extra pixels simply result in larger file sizes and longer upload times without providing any meaningful benefit.

For more on NFIQ scores, see Understanding NFIQ scores.

DPI vs. PPI

The terminology trips people up because scanner software uses one word and the standards use another.

• PPI (pixels per inch) is the correct term for a digital image. EBTS and ANSI/NIST-ITL 1-2011 are both written in PPI.
• DPI (dots per inch) is technically a printer term, but scanner manufacturers have used "DPI" for captured-image resolution for decades.

The same number goes in both places. Set the scanner to 600 DPI and you have produced a 600 PPI image. We use "PPI" when citing standards and "DPI" when describing scanner settings.

Color mode and file format

Two settings matter almost as much as resolution.

Grayscale. Grayscale scans are what the FBI's fingerprint pipeline uses (typically 8-bit grayscale, though 16-bit or other standard grayscale modes work perfectly fine as well). The WSQ compression used inside Type-4 EFT records (defined in the FBI's WSQ Gray-scale Compression Specification) is designed around grayscale fingerprint imagery. A color scan adds no information the matcher uses, and a 1-bit "black and white" or "line art" mode discards the ridge-edge detail that is the point of scanning.

PNG or TIFF - not JPEG. JPEG is lossy. Its compression introduces block artifacts around high-contrast edges, which is exactly what fingerprint ridges look like to the encoder. PNG and TIFF are lossless and produce a clean image the quality algorithm can score accurately. Save as PNG unless you have a specific reason not to.

Finding the settings on your scanner

Every scanning utility is slightly different, but the steps to configure these settings are generally the same. Open your scanner's software and look for a settings panel, often labeled Advanced Settings, Preferences, or Detailed Settings:

• Resolution / Quality: Locate the resolution field and select 600 DPI (or 600 PPI).
• Color Mode / Kind: Choose Grayscale (any standard grayscale setting like 8-bit or 16-bit is fine). Avoid "Color" or "1-bit Black & White / Line Art" modes.
• File Format / Save As: Select PNG or TIFF.

If the software only offers named presets (Text, Photo, Document), find the "Custom" or "Advanced" option that exposes a numeric DPI field. A preset alone is not enough. Presets often default to 200 or 300 DPI regardless of which one you pick.