Lindsay Lohan -- Baby Got Back ... Courtesy of Photoshop (PHOTO)

Lindsay Lohan is as good at Photoshop as she is community service -- not very.

LiLo posted a photo of herself striking an awkward pose, standing in front of a door. If you look closely ... you can see she altered the pic around the ass area, presumably to make it look more robust.

Lindsay captions the pic with an admission ... she cropped out her dogs because she didn't like the way they looked.