Female Ejaculation (i.e., 'squirting') is a natural reaction from a woman who has an EXTREMELY intense G-Spot orgasm. You might try running a search on the Board using any of the following terms:
Cytherea (the girl in the picture you posted)
Squirting
Female Ejaculation
My boyfriend has posted quite a few replies and informative articles about this particular subject.
And no, it's NOT pissing. It's an ejaculation of fluid very similar to semen (minus the actual sperm, obviously).