Hide a Message in a Photo

Hiding a message in a photo: a practical reference

What actually happens to the photo, how long a note can be, and how to make sure your recipient can still read it.

Method

LSB (least-significant-bit) encoding — the lowest bit of each pixel's red, green and blue value is replaced with one bit of your message. The alpha (transparency) channel is left untouched.

Visible change

At most ±1 on a 0–255 colour scale per channel — far below what the eye can perceive, so the picture looks identical.

Password option

Optional. With a password the message is encrypted before embedding using a key stretched from your password with PBKDF2 (SHA-256, 150,000 iterations) plus a random salt; without one, the bits are hidden but not encrypted.

Output format

Always a lossless PNG. JPG and WebP re-compress the pixels, which would wipe out the hidden bits, so the tool never exports those.

File size impact

Negligible content change — only one bit per colour is touched — though the saved PNG may differ in size from the original simply because it's re-encoded as lossless PNG.

How much fits

A typical phone photo has plenty of room. A 4032 × 3024 shot (a common 12-megapixel size) holds about 4,465 KB of text, and even a 1024 × 768 image holds about 288 KB — far more than a short note needs. The capacity meter shows the limit before you commit.

Security: it hides, it doesn't lock

Sharing it safely is about more than hiding. Steganography hides that a message exists; it does not, on its own, scramble what the message says. Anyone who knows to run this kind of image through an LSB extractor can read an un-passworded message. For real secrecy, set a password so the text is encrypted as well as hidden — and remember that LSB is not designed to survive forensic statistical analysis. If the photo will pass through other people or platforms before it reaches your recipient, a password matters: it keeps the note unreadable even if someone suspects the image is carrying one.

Tips that actually matter

• Send the downloaded PNG as a file/document attachment, not as an in-chat photo — most messaging apps re-compress inline photos and that destroys the hidden message.
• Pick a normal-looking everyday photo as the cover; an image that already looks like something you'd casually share draws no attention to itself.
• Agree the password with your recipient through a different channel, never inside the same photo or message.