Actually there is no special difference , if to say about pictures .
But by the word фотография we can point all issue referring to profession , making photo , chemical process of it ... by word снимок -it is impossible.
Я зарабатываю фотографией- i earn money by photography ( to say truth- i do it actually) .
Я делаю снимки - i make pics.
Мне понравилась фотография - i like the photography - here i can refers to a concrete pic. or to all issue of photography , depending from context.
Мне понрафился снимок - it is always to a concrete pic.
also as photographer slang i can say about a photo pic- отпечаток , картинка , карточка. фотка ( most common slang between non-professional )