[__MatrixMan__]

The trouble with pictures is that when you share them online the platform will likely compress them before serving them to others, spoiling your steganography. I think text-in-text is the way to go. Decrypt that recipe for brownies into the actual message. For example: https://arxiv.org/abs/2510.20075

[Bender]

One can host their own private or semi-private forum, chat server, chan board, etc... and choose not to re-encode the images and/or permit .tar .7z .zip archives and so on. Keep the bots away with basic auth to minimize skiddie risk to platform RCE's.

It's unlikely people can move their friends to their own platform but the best way I have found is to call it a "fall-back" platform for when Discord and others are temporarily offline. Get people used to the idea that is the place to share things they do not want leaked when the big platform 3rd parties expose files. The admin can encrypt the storage and periodically zero out files and zero out empty space for privacy.

People with slightly higher opsec may choose to block mobile proprietary devices.

[__MatrixMan__]

Joining a private space that's set up for steganography, or facilitating such a space either by self hosting or by logging in somewhere as an administrator, is sort of at odds with the nothing-to-see-here approach that steganography takes. An adversary that has compromised one message can then use whatever metadata is intrinsic to that space to suss out which other plaintexts might contain a secret, and which other humans might be exchanging secrets in that place.

The ideal hiding space would be visible to the public, and indistinguishable from a mountain of other material that's visible to the public--especially if they don't have to log in to see it. That way if a message is found, the search for co-conspirators doesn't narrow at all.

[Bender]

In that case I think you may be out of luck as most platform change the images. Sometimes they just remove exif data but some compress or optimize in their view the images. In that case maybe find a public site that allows archive files.

[__MatrixMan__]

My point is that text is a better medium for this anyhow.