'Frozen' Look-Alike Claims Nude Pics Are Too Fat to Be Her!

Anna Faith Carlson, the model who's a dead ringer for Elsa from "Frozen," is claiming a website posted fake nude pics of her ... and says the proof is in the waistline.

The site Celeb Jihad posted a bunch of "before-and-after" nude selfies it claims are Anna showing off a recent boob job. The pics show a topless woman with tan lines, and bandages under her breasts. It appears to be a post-op shot.

Anna's team claims that's not her in the pics, insisting the nude chick is "much heavier than Anna has ever been in her life." They added, Anna is in "great shape with a very small waist" ... unlike the alleged impostor.

They say there are also differences in the nose, teeth and face that prove Anna's NOT the nudie pic chick. Her camp is threatening to sue if the post isn't deleted.

So, no -- she's not willing to let it go.