Welcome.
Most content licenses specify that the photos (or whatever) can be used on x number of domains on the internet. Since your eBook is on the 'net and not in print, your use of those images PROBABLY complies with the terms of the license. I emphasize
probably because common sense would say that such use is legal - but common sense and the law don't always go hand-in-hand.
I know that an attorney frequently answers questions like this at
The Adult Webmaster. He also invariably includes the fact that opinions offered on a message board are not and cannot have the force of an attorney-client consultation because there are too many variables. So, you can
* assume its okay and use them, and have common sense on your side;
* ask the person you purchase the images/? from and get their response in writing; or
* consult an attorney.
I'm kind of paranoid about this kind of stuff, but I'd feel safe in this instance in going with the 2nd option of asking the person you are licensing the images from.
I really did want to be a lawyer - but they turned me down when they found out my parents were married to each other.