Out of the big three, Google Drive had an insanely good run as unlimited. (Even non-enterprise business plans with caps in theory were unlimited in practice until this year.)
- Former ACD customer who got burned.
I assume this means they look at your photos and other data.
You can "compress" anything, if one of the modes of your compressor is simply to store the data "as is", but generally speaking encrypted data is indistinguishable from a random bit stream and cannot be compressed.
If you think about it, one of the ways that compressors and attacks on encryption work is by looking for structure in the data. If you still have that after encryption, you don't have a good algorithm.
Due to the pigeonhole principle, to be able to make some inputs shorter you have to make some inputs longer. The way compression works is by making more likely inputs shorter, while making unlikely inputs longer. But for encrypted data, if your encryption method is good (that is, not ECB mode), all possible values are equally likely (unless you known the secret key).
Mostly it's photos, pdfs, word documents, executables, videos, etc.
Aside from that there are mathematical tools you can use to detect whether a binary blob is compressed/encrypted or not, like entropy calculation.
That gives me an idea. Might be fun to write a tool that will encrypt a file but make it look like a valid .zip file that just unpacks to meaningless noise. There's gotta be something like that already out there... Although you could recursively unpack/evaluate and eventually you should get to the point where it's non-random data. If you never do, then it's encrypted.
There are some academic papers (I think one by Ross Anderson) which state that steganography relies on there being some randomness in the data you are hiding the message inside. So, to make the bandwidth available for for steganographic data hiding as large as possible, those needing to conceal data need incentives for innocents to publish files constructed using as large as possible quantities of random bits. It looks like Stable Diffusion is providing this incentive!
I used to use Amazon stuff but it has really become such insane spyware. There is no data collection/analytics that goes too far for Amazon. It's really appalling, no less so that they use their near monopoly on using Kindles to deeply mine for data on exactly what people are reading, how long on each page, etc. Really gross.