Your question is certainly both interesting and very important. The question of the physical aspect, yes - SEX! - is still hugely underrated, understated and hence underestimated. Sex is and remains the paramount reason for couples to date, to mate and to stay together.
If anyone has doubts, here's the ultimate relationship health checker:

Sex minus quarrels equals the state of health.

Many people (women AND men!) look very different on photos from the way they do when they appear on camera or in real life. Some manage to look better, others are less photogenic, so of course there is a natural interest in what the potential spouse may look like in their entirety.
However, if the ONLY topic is sex, melons, wieners and the kama sutra up and down, then it is very doubtful whether the person is serious about their intentions.
If you happen to have plenty of conversations on a diverse number of topics, share a wide range of interests and eventually end up talking about sexual habits and preferences because you have developed such a high level of trust and profound mutual understanding, such photos are acceptable, under the condition that both, he AND she feel comfortable with sharing them.
Asking is always OK, and so is declining. 😊 

Have a great time here and happy dating (or sharing photos   )