Put something inside a picture, where it does not look like anything.
Drop the picture to hide it in
or tap to choose · a busy, detailed photo hides more than a plain one
…or hide a whole file
any file at all · a photo, a recording, a document
Drop the picture to open
or tap to choose · it must be the PNG saved from here, not a re-shared copy
Drop a picture to examine
or tap to choose · estimates how much of the low bits carry something
What survives, and what destroys it
Save and send the PNG exactly as it comes out of here. The message lives in the very lowest bit of each colour, and anything that re-encodes the picture wipes it.
JPEG destroys it completely. So does resizing, cropping, rotating, a filter, or a screenshot of the picture.
Most places you would post it re-encode on upload. Messaging apps and social platforms nearly always do. Sending the file as an attachment or a document, rather than as a photo, usually survives.
Cloud drives, email attachments and USB sticks are fine, because they move the file rather than the picture.
What this is and is not. With a passphrase, the message is encrypted before it goes in, so finding it is not the same as reading it, and even the pattern of which pixels were used depends on the passphrase. Without one, anyone who suspects something is there can pull it straight out. What this cannot do is hide the fact that you sent a picture at all, and a picture with a large payload in it can be detected as suspicious even by someone who never reads a word of it. The Check tab runs that same detection on your own work, so you can see what you are up against rather than take anyone's word for it.
How it works: every colour in a picture is a number, and changing the last bit of that number shifts the shade by an amount no eye can see. Write your message across enough of those last bits and it is simply there, in a picture that looks unchanged. The care is in the choosing. Flat areas of a single colour make changes stand out under the right test, so this picks busy, textured regions where the change disappears into the detail, and it walks them in an order derived from your passphrase, so that without it there is no way to know which pixels to read or in what sequence. Everything happens in this page. The picture is never uploaded and neither is the passphrase.