Every day. Sometimes more. The odd time maybe not for a few days.
Mainly watch videos these days. Used to be pictures, but that was mainly before videos became so ubiquitous and broadband arrived (not in that order). Sometimes now images are what I choose. Subject matter wise it's mainly wife/gf, voyeur, public, clothing, ...not sure I can list it all in any sensible way.
Thoughts that I have that definitely lead to orgasm are usually about my wife and her having fun/climaxing. The best are based on historic events, for example a current favourite is thinking about when she was out in a local town and she almost got fucked in a carpark stair well.