Bit-plane viewer

One bit of one colour channel, drawn as a black and white image the same size as the original. For every pixel, the chosen bit of the chosen channel is read; a 1 becomes white and a 0 becomes black, and the alpha of the output is fully opaque. Noise-looking static is normal for low bits of a photo. Visible shapes, text or blocks in a low bit-plane are what you are hunting for.

Start where the defaults are, channel red and bit 0, since bit 0 is the least significant bit and the usual place data is hidden. Then work through green and blue at bit 0, and try alpha if the image has one. Higher bits carry the actual picture, so bit 7 looks like a hard-thresholded version of the photograph.

A PNG named after your file with the channel and bit appended, so photo-red-bit0.png. It is the same width and height as the input, so you can flip between planes and compare them, or line one up against the original.

Because JPEG is lossy, and the bit-planes you are seeing belong to the decoded output, not to whatever the image held before it was compressed. Any LSB payload that existed before a JPEG save is destroyed by the quantisation. Bit-plane inspection is meaningful on lossless images: PNG, and WebP when it was encoded losslessly.

JPG, PNG and WebP, chosen by the file extension. Anything else is refused with a message naming your file and stating that only JPG, PNG and WebP are supported. Rename or convert first if your file is a BMP, GIF or TIFF; Convert image handles that.

Run LSB steganography extract, which reads the same bits as a bitstream and reports any runs of printable text it finds. A pattern in a bit-plane is a strong hint that something is there, and it is not proof of a hidden message: heavy editing, resizing, dithering and some encoders all leave structure in the low bits.