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Sorry, but your termnology misses the mark by a mile. A Pro is someone who makes his living at something while an amateur doesn't. There are a lot of pros who suck ass and a lot of amateurs who have loads of talent, they just don't get paid for it. Hobbyist and amateur are synonyms. An artist is pretty much anyone producing, or trying to produce, art.
However, that said, there is a difference between casual shooters and serious photographers. Casual shooters are the ones who shoot their son's third birthday party, the family standing in front of the Grand Canyon, and so on. They are recording personal memories to share with families and friends. They produce snapshots. Serious photographers come in two varieties.
The first of these varieties are the Fine Art Photographers. They are intent on producing artwork, which will be viewed by strangers who will percieve them as artwork. They use creativity in their work, use enhancements and special effects in photoshop, even add things from other images. Landscape artists, portrait artists, illustrators of fiction, and creators of fine art (among others) fall into this category.
The second of the two varieties is the documentary photographer. A documentary photographer produces images that purport to tell the absolute truth. Creativity is discouraged in documentary photography and photoshop is only used to bring the photo as nearly back to what the photographer originally saw in his viewfinder as possible. Photojournalists, forensic photographers and the illustrators of technical articles and documentaries fall into this category.