I'm not sure how many takers you will get on this one - the question is as tough to answer as "what is the definition of beauty?." But I hope you get some thoughtful responses. The answer to this question will be (by definition) biased and personal. Here's my answer...
I think guys have been hard wired to be somewhat superficial in our initial assessment of a lady (breasts, butt, legs, general physique, etc.). So ladies, if I am ever a shallow bastard I blame evolution for making me that way. LOL. OK, if I'm being honest I would say a nice, round butt really catches my eye first. Then overall skin tone - if a lady has beautiful skin that is a big attractor for me. Then eyes, lips - pretty smile, hair, legs, feet, and breasts. More or less in that order.
It sounded like the question was strictly from the standpoint of looks - making a judgement to see a lady solely from seeing her picture, but I would argue there is something more important that can't (usually) be derived from a picture - attitude. To me attitude is much more important than overall looks. And to keep me coming back a woman has to have a playful, creative, mischievous, adventurous vibe. The twist is - I really don't know what her energy is like until I have met with her at least once (although I've known a special few where their personality started winning me over from that first email exchange).
On that note, I would just point out to the ladies that first impressions are forever. If you want to set yourself apart from the rest (that's the whole game, correct?) then put some thought into your correspondence in addition to your pictures. I'm not expecting any literary masterpieces but even in a few sentence email you can throw something interesting or funny in. I can't tell you how many times I've put together a well worded paragraph or two introducing myself to get a one sentence "sounds good - later" type of response. Remember ladies, we seek you out for one reason - for you to make us feel special.
Just keep eveeything in perspective. A pretty picture showing your physical attractiveness may bring us to your door, but it's your attitude and performance that will keep us coming back.