Why Dotspotter Fails to Detect Yellow Dots on Your Uploaded Image

Updated

Dotspotter (forensicdots.de) needs a very specific kind of input to find the yellow dot code (MIC) on a scanned page. If it returns no result, the usual cause is that the scan or the printout doesn't match those conditions. The most common culprits are a scan that isn't exactly 600 dpi, a scan that isn't in color, or a JPG that was resized or compressed too aggressively. Fixing those three things resolves most failures.

The input conditions Dotspotter depends on

Dotspotter works by analyzing a scanned image for a faint yellow dot pattern. That pattern is low-contrast and pixel-level, so the tool is sensitive to anything that changes resolution, color depth, or pixel values.

Requirement What Dotspotter expects What breaks detection
Printer Color laser printer Inkjet or mono laser output
Page content Mainly white Busy or dark pages
Scan resolution Exactly 600 dpi Lower or higher dpi
Scan mode Color, photo quality, 24-bit depth Grayscale or black-and-white
File format JPG Other formats
File size Under 10 MB Oversized files
Image handling Cropped if too large Resized or downscaled

Check the printout first

The dots are printed by the printer, so a bad printout can't be recovered by a good scan.

  • Use a color laser printer. The tracking dot pattern is a feature of color laser output. An inkjet print or a black-and-white laser print won't carry the code Dotspotter looks for.
  • Keep the page mainly white. A page full of text or images makes the faint dots harder to isolate. Dotspotter provides a test sheet (dotspotter-test-sheet.png) you can print if you want a clean, mostly white page.
  • Print on a real page, not a screen. The code is physical output, so a screenshot or digital file won't work.

Check the scan settings

This is where most failures happen.

  • Resolution must be exactly 600 dpi. Not 300, not 1200. The dot pattern is resolved at a specific scale, and other resolutions misalign it.
  • Scan in color with photo quality (24-bit color depth). Grayscale or bitonal scans discard the color information the yellow dots depend on.
  • Save as JPG at high quality. A low-quality JPG setting throws away pixel detail, and the dots are exactly the kind of fine detail that gets lost.

Check how you handled the file size

If your scan is over 10 MB, the instinct is to shrink it — but how you shrink it matters.

  • Do not resize or downscale the image. Reducing dimensions destroys the dot pattern.
  • Do not lower the JPG quality to shrink the file. Heavy compression blurs the faint dots beyond recovery.
  • Crop instead. Cutting away empty margins reduces file size while keeping the dots at full resolution and quality. This is the method Dotspotter itself recommends.

Give it time before assuming failure

Dotspotter can take up to several minutes depending on image size. The tool is finished when a second image appears on the right side of the page. If that second image hasn't appeared yet, the analysis is still running — not necessarily failing.

A quick troubleshooting order

  1. Confirm the page was printed on a color laser printer and is mostly white.
  2. Re-scan at exactly 600 dpi, color, photo quality, 24-bit.
  3. Save as a high-quality JPG under 10 MB — crop rather than resize or compress.
  4. Upload and wait for the second image to appear on the right.
  5. If it still fails, re-check the scan resolution and color mode first; they are the most frequent causes.