If you use the ghost app regularly, you've probably seen this feature by now -- it's an augmented reality lens you can throw onto your mug, changing your facial expression to one that's hilariously sad and emotive ... and it's got the kids hooked, as lots of these videos have now gone viral.

While it might be a hit ... it's also become the cause of a new rumor/joke -- namely, that the Snapchat heads must've used Amber's crying last week on the stand as the blueprint here.

Despite the rampant speculation, we're here to tell you otherwise ... a spokesperson for Snap tells TMZ there's simply no truth whatsoever, that the lens is inspired by Amber Heard and if you think about this logistically -- it just doesn't add up.

We're told that this specific filter -- which just dropped Friday -- has been in the works for 6 months ... so it was being developed well before Amber ever offered her tearful testimony. More importantly, Snapchat tells us they'd never play coy with a DV case.

Another tell that this has nothing to do with Amber ... the fact Snap dropped a filter that does the exact opposite not too long ago (big smiley face), so naturally -- sad face would follow.

Like we said, the crying face filter is all the rage since its debut last week -- it's already amassed upwards of 1.3 billion impressions on Snapchat, we're told -- and it was especially used in NFL circles, where some of the league's biggest stars were having fun shedding fake tears for their followers and friends ... and to be honest, it's pretty freakin' funny.