They don't mention cipher mode, hash algorithm, hash tuning parameters, or if they are even using authentication of some form alongside the encryption.
Complete transparency in terms of crypto ensures you aren't holding a steaming pile of shit if the service becomes popular and it is found that you were using ECB and SHA1.
You MUST trust the software you feed your unencrypted data to. And if that softare is downloaded each time from the web, it's rather hard to do.
To all the naysayers: You're right that you have no reason to trust ANY online tool or channel with your secret documents. Open source is best, etc. But, this crypto tool is more about hiding data than securing it. So, for instance, maybe you don't care if this site "steals" your resume as long as your boss doesn't see it. So, relying on their encryption works for that. Still, if you want to keep secrets from everybody, just encrypt your files before hiding them with this. Either way, pixelator is still a viable (and kind of fun) tool to use.
That said it looks like it does it all client-side (but I'm not 100% sure -- could we get a confirmation on that?)
A search for steganography on github lead to projects like darkjpeg that are open-source.
