Photo-manipulation can be very effective. There are some fine examples at BDSMartwork. Even so it still takes practice to get very good quality.
Have you tried 3D "figure-posing" programs?
They are relatively easy to get into, but do require some work to get top quality images from. Try Daz studio, I believe that is free.
Too "fiddly" for me, I'd rather draw, but I have seen some good work created in such programs.
There are also many photo-tracers who submit art here. Instead of simply combining photos, they literally trace parts of the images that they need and combine them in their finished "drawing".
Again a fiddly time consuming exercise for those who can already draw, but for those who can't, some have developed this approach to a high art, with practice of course.
Whichever way you go, don't give up, the more BDSM images here the better.