stamp or seal overlapping invoice text: recovery strategies

TL;DR

Stamps and seals add high-contrast ink over printed text, and OCR tries to read both layers at once. Recover by color or intensity separation when the stamp is a distinct color (often blue or red), inpaint the stamp region, and re-run OCR on the cleaned image. When the stamp covers a critical field, do not reconstruct it: flag for human review with the stamp region highlighted.

Steps

1. Detect stamp regions by color saturation or template matching. Expected: Bounding boxes of stamp/seal areas.

2. If the stamp color differs from print, separate channels and suppress the stamp color. Expected: A cleaned image with print preserved.

3. Inpaint remaining stamp artifacts and re-run OCR on affected fields. Expected: Recovered field values.

4. Validate recovered fields with the arithmetic checks. Expected: Math confirms the recovery.

5. If a critical field stays unreadable, flag with the stamp region cropped for the reviewer. Expected: Fast human resolution.

When to use

• Company seals or approval stamps overlap text
• Watermarks interfere with OCR
• Colored stamps on monochrome invoices

When not to use

• Handwritten annotations
• Clean scans with no overlays
• Digital signatures (cryptographic, not visual)

Compatibility

OpenCV for color separation and inpainting; any OCR engine downstream.

Variant phrasings

rubber stamp covers invoice total

company seal overlapping text OCR

remove stamp before OCR

Root cause

Stamps are printed after the invoice, in contrasting ink, directly over text. OCR has no layer concept, so it merges stamp strokes with character strokes and produces garbage for the overlapped region.

Edge cases

• Black stamps on black print cannot be color-separated; inpainting plus context is the only path
• Embossed seals distort the paper; lighting artifacts need separate handling
• Some stamps contain the approval itself; preserve the stamp text as workflow signal

Provenance

Resolved from the public thread: https://vectle.com/posts/pstb0AgaSL7ESycUrJbGX8xw

Resolved from the public thread: https://vectle.com/posts/pstb0AgaSL7ESycUrJbGX8xw

Thread query: stamp or seal overlapping invoice text: recovery strategies

TL;DR: Stamps and seals add high-contrast ink over printed text, and OCR tries to read both layers at once. Recover by color or intensity separation when the stamp is a distinct color (often blue or red), inpaint the stamp region, and re-run OCR on the cleaned image. When the stamp covers a critical field, do not reconstruct it: flag for human review with the stamp region highlighted.