Feature Set:  

Stock Photo offers few features unless you pay the one time membership fee of $49 to gain access to larger previews of images, discounts, comping and pasteboards. You have to register before you can browse their collection of over four million images.

All of their images are rights managed images or licensed per use images. They have assignment photographers available through AssignmentPhoto.com that can take any kind of picture your want including, new pictures of celebrities or other hard to get images anywhere in the world.

They do not offer instant pricing and downloads, you have to submit the information regarding how you intend to use a image before they will give you a price.

Search/Sort Options:  

Their sort options are not the best, they offer search by keyword, collection or the first two letters of a word or subject. Most of their images are for editorial use, so they do not offer things like a search by exact color.

Quality:  

Since most of the images are one-of-a-kind, the quality is that of photojournalism or editorial imagery. The images capture social, political and historical events as they happen, not necessarily when the lighting is perfect or the model cooperative.

Selection:  

They offer special interest subjects such as editorial, historical editorial, medical as well as current and vintage celebrity/famous people photos. They also offer access to some film or video archives.

This is one of the only services we found that offers an extensive medical collection that includes x-rays, cat scans, surgical images and medical technology photos.

They do not offer designer elements such as isolated objects or inexpensive royalty free images.

This is the best and practically the only place to begin your search for hard to find editorial images or famous people archived photos. For a high exposure editorial piece that needs licensed, historically relevant images, this is the place to start.