I recommend spending time at marbles shows handling marbles and discussing the many variants of a single type with experienced collectors. Learning to ID marbles from photos is the pathway to mis-identification. I am convinced that the reason Ebay is so full of mis-identified marbles is that inexperience people buy a book (or look online) and try to match what they have with the closest looking marble (usually by color alone) that is worth a lot.
There is no substitute for handling tens of thousands of marbles and looking at their nuances and variations to get a feel for the fine art of identification.