This is an example of 2 camera mapping technics but using very few time to do. The bump textures are realized with Gimp and Insane Bump addon.
In the first case, it is better to have a bump map but you don't need to do a complex mapping (only one vertical and horizontal plane), and just a simple projection is enought.
For the 2 case (under water), complex mapping is not required as well, but you just need to do some few approximate manual displacement on the plane where you think the objects are (use sculture and push a bit where it is needed).
Result is not perfect but the time spent is very fast.
If you want to see more quick tutorials, please consult my channel here: / freelandertrail
On this page of the site you can watch the video online Blender easy Camera Mapping for beginners (Quick Tutorial) with a duration of hours minute second in good quality, which was uploaded by the user FreelanderTrail 05 July 2014, share the link with friends and acquaintances, this video has already been watched 1,602 times on youtube and it was liked by 11 viewers. Enjoy your viewing!