Each colour of a pixel (red, green, blue) is a number from 0 to 255, written with 8 bits. The tool isolates one of those bits across the whole image: a bit plane, shown in black and white. High bits draw the picture; low bits look like noise… unless someone drew something there. Paste the address of a Lab image or choose a file.

or choose a file

In real life: StegSolve, Aperi'Solve, StegOnline (« bit planes »). A CTF classic: text or a QR code hidden in one specific bit of a single channel, which LSB text tools cannot see. It only works on lossless images (PNG, BMP): JPEG compression destroys the low bits.