It depends on what you purchase. Purchasing the Photo CD will include a copy of every picture in your account, including all edits. If you simply do normal Photopass, this will primarily be pictures taken in the parks and with characters.
However, pictures taken at certain locations will add "bonus" pictures to your account. These are typically stock photos that will be included on the CD. For instance, when we added the pictures taken at AK last trip, we ended up with several photos of one of the Tamarins (sp?). And some picture we had taken in the MK added some pictures of Mickey & Minnie. (It may be a general MK picture, or it may have been that we met Mickey and Minnie. No idea) They have also released codes for Halloween photos, Christmas photos, etc. The normal Photopass also included the picture from Test Track for free. As of now, no one knows if this will return when the ride re-opens, although I imagine it will.
The Photopass+ product includes all of the above, but will also include a CD with 300-400 stock photos from around the parks. And you will also be able to claim and ride photos and dining photos while the Photopass+ is valid. You can also buy the stock photo CD for something like $39.95 if you really want it.