http://status.nowherejezfoltodf4jiyl6r56jnzintap5vyjlia7fkirfsnfizflqd.onion/opsec/steghide/index.html
Make sure to only use this with originals only you are in possession of - in a pinch, adding an in-picture caption, resizing it, etc. offers plausible deniability, as different image editing programs are notoriously variant in handling pixel-level details. Avoid images with little detail: Images without pixel-level visual noise (e.g. diagrams, images of text, etc.) will have less hiding space, and become visible deteriorated when files are embedded.