> can pass through any channel that accepts images
No. Any online service worth its salt is going to reencode images to serve proper sizes and maybe do other processing. Along the way stuff like EXIF data and other worthless (for displaying the image) chuff will get stripped from the image. Alternatively, if you mean not somehow embedding in the file but encoding in the actual pixels of the image, that data will get lost as well when the image is resized and resampled. To survive most image manipulations, the data will have to be quite crude and you'll have low bandwidth with this kind of encryption.
An exception would be some photographer oriented services like Flickr that allow you to download the original file but those are a minority.
Yes. Any algorithm designed to be resilient to common processing steps will pass this test with flying colors. Also, EXIF data is not used in steganography, by definition.
Hence why I mentioned that if you encode the data in the actual image (the part that's guaranteed to survive processing,) you cannot do it with very fine elements, like subtly shifting the colors of individual pixels or the like, because an average Facebook JPEG algorithm, for example, will just destroy that. You need to use data points that could survive heavy JPEG artifacting, and that means very few data points per image, and low bandwidth.
That’s a moving target with no guarantees to stay true. Steganography in the use cases you’ve described adds complexity and additional portability challenges over a plain encrypted file.
No. Any online service worth its salt is going to reencode images to serve proper sizes and maybe do other processing. Along the way stuff like EXIF data and other worthless (for displaying the image) chuff will get stripped from the image. Alternatively, if you mean not somehow embedding in the file but encoding in the actual pixels of the image, that data will get lost as well when the image is resized and resampled. To survive most image manipulations, the data will have to be quite crude and you'll have low bandwidth with this kind of encryption.
An exception would be some photographer oriented services like Flickr that allow you to download the original file but those are a minority.