This thread provides some "clues" that might help:
http://www.yorkietalk.com/forums/showthread.php?t=16045
Other than that, looking at the parents and previous litters that have now matured are a guide too. Pictures alone are difficult to see puppy potential. A tilt of the head, a different angle of the camera -- all can mislead and hide a multi-tude of "faults." I have pictures of my two that make certain features look entirely different. My larger, longer-legged female can look just as small and squat as my male, depending on the angle. Their colors can look almost washed out with too much light and darker than real if the lighting is poor. No substitute for seeing them in person!
Look hard at puppies from good lines, so you know ahead of time what to expect. Even poorly bred pupppies can look so adorable! I had a difficult time with one -- she was obviously not a good breed representative but she was the cutest thing and so loving -- I bought her anyway and had her spayed. I was never sorry as she was a wonderful pet. But when I got Ben and Sadie, I wanted to ensure they at least had the potential to be breed standard. That is the look that first made me seek out Yorkies instead of another breed. So, I was more particular and so far have two that seem to be maturing very nicely. I do not know yet if they will be show/breeding quality but they definately look like Yorkies.
