There's a photo making the rounds this morning featuring Jesse James hanging out with a woman said to be Sandra Bullock on Monday  ... but TMZ has learned, it definitely ain't Sandy.


The photo in question shows Jesse walking into West Coast Choppers with a mystery brunette lady ... but the photo only shows the couple from behind -- meaning NO FACES.

But sources at WCC tell TMZ that Sandra has not been around the shop for a long while ... and she definitely wasn't there on Monday.

So who's the mystery woman??? Sources at WCC tell us she's Hildie Katibah (pictured above) ... the head of Pay Up Sucker Productions ... which is affiliated with Jesse's bike business. 

So, sorry to all those people rooting for a reunion, but it hasn't happened ... yet.