That is correct. If the NSA or any other organization really wants to read your message, it will be able to. There are several ways to accomplish this (including what you just mentioned as well as the image sifting and OCR method I included above), but some of them just involve more work/modification-of-strategy than others.
Comments
I'm assuming you secure the image URL with HTTPS at least to minimize the chances that an ISP could intercept it on the wire?
Nope. SSL MITM via CA.
That is correct. If the NSA or any other organization really wants to read your message, it will be able to. There are several ways to accomplish this (including what you just mentioned as well as the image sifting and OCR method I included above), but some of them just involve more work/modification-of-strategy than others.