Image Watermark
Block luminance steganography writes the recipient token into the average brightness of 8x8 blocks in the Y channel of YCbCr, with Reed Solomon parity and three redundant copies. The watermarked image is returned as lossless PNG, and the mark survives a JPEG round trip, so a screenshot saved as JPEG still names the recipient.
Carrier capabilities
- Stego mode
- Robust Block (JPEG resistant)
- Survives
- JPEG at quality 70 and above, saving again as PNG, moderate resize, mild colour adjustment
- Does not survive
- Heavy JPEG below quality 50, crop of more than half the frame, heavy blur
- Engine
- Pillow yes · numpy yes · reedsolo yes
Embed
Detect
Embedding profile
- Carrier
- Average luminance of 8x8 blocks, Y channel of YCbCr
- Modulation
- Quantisation index, step 12, offset 6 for a set bit
- Payload
- 16 bytes, recipient token, plus 10 bytes Reed Solomon parity and an 8 byte frame header
- Redundancy
- 3 copies on disjoint block sets, majority vote on recovery
- Output format
- PNG, lossless
- Visual delta
- Up to 6 luma levels per block, below perceptual threshold on photographic content
JPG and WEBP uploads are converted to PNG before embedding. Download the watermarked PNG and upload it here to recover the recipient. Saving the download as JPEG at quality 70 or above keeps the payload readable, which is the point of this carrier. The scanner tries the block luminance engine first and falls back to LSB.