I combined two stock photos I purchased from Fotolia into one graphic (I presume this would be considered a derivative), and on my (non-commercial) website I carefully attributed both of the pics I used to the best of my ability.
My understanding is that I cannot give anyone else permission to post the resulting graphic on their own website, even though I "created" it by combining those two pics, because I can in no way "transfer" any type of copyright to them. Is this correct?
Generally, with purchased stock photography, you don't need to attribute any photos you purchased. That's the whole point of stock photography.
However for resale of images created with stock photos - that would include things such as selling prints, or supplying image files, and depending on what the licences say of course, you often have to buy an extended licence, which is more expensive.
Having never used the service you named, I have no idea what licences they have available for purchase. You'll need to check this yourself. Perhaps search their site, or if you can't get a straight answer, call their customer support and ask the question. Tell them what you need the images for, and they should be able to suggest the correct licence to buy.
Disclaimer: I am not a lawyer, and my answer is not legal advice. If you want legal advice, hire a lawyer.
Yes. That is correct.
You purchased a license to use the images. You can not give anyone else permission to use the images. If they also purchase the two images, then you could allow them the use of your composite if you desire.
