I mainly use my own photographs for photo manipulation, either those already collected or deliberately taken of odd things. Sometimes it is difficult to obtain an image without special equipment.
Two instances of this are used in the flying beetle invasion - a grain of pollen and a flying beetle downloaded from copyright free web resources.
I use an oldish version of "Photoshop" or the latest version of "GIMP". This can be downloaded free of charge to run on any operating system.