Hide Text in an Image

Every pixel stores red, green and blue values from 0 to 255. Changing the last binary digit of a value changes it by at most 1, which is not visible to the eye. This tool writes your message into those last digits, the least significant bits, one bit per colour channel and three bits per pixel.

The message is stored as UTF-8 text, so accents and other alphabets work. It is preceded by a short marker ("IYORK") and its length, which is how the Reveal mode knows where a message starts and ends. Only fully opaque pixels are used, because the browser can alter the low bits of semi-transparent pixels.

Each opaque pixel holds 3 bits, so 8 pixels hold 3 bytes. A 100 x 100 image (10,000 pixels) can carry 3,750 bytes, minus 9 bytes for the marker and length. Most photos have millions of pixels, so space is rarely the problem; the tool tells you if a message is too long for the image you chose.

The hidden bits survive only as long as the exact pixel values do. Any of these destroys them:

• saving the image as JPG or WebP, or uploading it to a service that recompresses it, which includes most social networks and many messaging apps;
• resizing, cropping, rotating or applying a filter;
• taking a screenshot of the image.

Share the PNG as a file: by email attachment, cloud storage link or a file-transfer service that keeps files unchanged.

Anyone with this tool, or anyone who knows to look at the low bits, can read the message. There is no password and no encryption. Statistical analysis can also reveal that an image has been modified this way. For anything confidential, encrypt the text with a proper encryption tool first and hide the encrypted result, or do not use an image at all.

Choose a PNG or BMP image. The output is always PNG, because PNG is lossless. Images created with an earlier version of this tool may not be readable, because that version wrote the bits in a different order than it read them. Hiding and revealing both run entirely in your browser; neither the image nor the message is uploaded.