Looks like three pictures of the same flower (or similar flowers?) superimposed. You can use layer blending modes and opacity to control how they will blend, it's fairly easy stuff. Some cameras offer you the possibility of multiple exposures in-camera and in RAW as well.
The most common blending modes are multiply and screen. Multiply will make all white pixels transparent depending on their luminance (right?) value. Screen would do the same but for black pixels. You can play with high key and low key images this way.