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I guess this would be useful with Amazon's free unlimited cloud photo storage.

A small (631 bytes) JPEG concatenated with your file of choice (preferably encrypted) accomishes what you're thinking.

But you run the risk of a ToS violating, losing your files and having your account banned.

Only if they leave the photo as a losslessly compressed png. They might convert to a lossy JPEG on upload, which means your data is toast.

Two can play at that game. You can store data in JPEG that can even survive recompression with lower quality. If it's worth it to you to go to all that trouble, that is.

Interesting paper: Bypassing Cloud Providers’ Data Validation to Store Arbitrary Data [1]

>JPG & PNG Steganography Encoder (JPG-PNGStega). The purpose of this encoder is to inject data (hiding it) in JPG and PNG files. It takes a File Format Sample (JPG or PNG) and, for each pixel, it injects 3 bits of data in the LSBs (Least Significant Bit). There are more sophisticated image steganography methods already widely discussed. However, the use of this encoder shows that even basic meth- ods of JPG and PNG steganography are possible in SaaS applications, and the exploitation of such method may bring impacts

http://arxiv.org/ftp/arxiv/papers/1404/1404.2637.pdf

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