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How to hide a secret message in a picture
You can put a line of text inside an ordinary photo so that the image looks unchanged, and read the text back later. This is called steganography. Below is how it works, why hidden messages often vanish after sending, and how to do it on a phone.
How text fits inside an image
Every pixel of a photo stores its color as three numbers: red, green and blue, each from 0 to 255. Changing one of those numbers by 1 shifts the color by an amount the eye cannot see. The most common technique, LSB (least significant bit), uses exactly that: the message is turned into bits, and each bit replaces the lowest bit of a color value.
The capacity is large. With one bit per color channel, a 1080 × 1080 photo has about 3.5 million spare bits — far more than any text message needs.
Why hidden messages disappear
LSB data lives in the finest details of the pixels, and those are exactly what compression throws away. When you send a photo through Telegram, WhatsApp or most social networks, the service recompresses it to save traffic, and the hidden bits are overwritten. The picture looks the same; the message is gone.
- Survives: sending the image as a file or document, email attachments, cloud storage, USB transfer, PNG files.
- Usually destroyed: sending as a regular photo in messengers, posting to social networks, screenshots, editing or resizing.
How to do it on your phone with Underlayer
- Open Underlayer and choose a photo — or share a photo to Underlayer from the gallery, camera or another app.
- Type the message.
- Pick a mode:
- Hidden — the message goes invisibly into the pixels (LSB). Use it when the image will be sent as a file, without compression.
- Open — the message is encoded as a thin colored frame around the image. The frame is visible, but it survives Telegram and WhatsApp compression.
- Save or share the result. To read the message, the recipient opens the image in Underlayer.
JPG, PNG, GIF and WebP work for both hiding and reading. Everything runs on the phone: no account, no upload, no internet needed.
Hiding is not encrypting
Steganography hides the fact that a message exists, but it does not lock it. Anyone who suspects a hidden message and runs a decoder can read it. If the text itself must stay confidential, encrypt it first and hide the encrypted text.
Ideas for using it
- A note or a riddle inside a photo for a friend or a scavenger hunt.
- A quiet watermark — your name or a date inside your own pictures.
- A short message that does not stand out in a shared photo album.
FAQ
Can someone tell that a photo has a hidden message?
Not by looking at it. Statistical analysis tools can sometimes detect LSB changes, which is another reason to encrypt anything sensitive.
Why did my message disappear after sending?
The messenger recompressed the photo. Send it as a file, or use Open mode.
Does Underlayer upload my photos?
No. Hiding and reading happen entirely on the phone.