Famed celeb photographer Terry Richardson posted a photo of Lady Gaga last night ... sporting a giant rock he claims is her engagement ring.

Gaga herself has said nothing about the ring (and by "said" we mean "tweeted") and there are conflicting reports about her dating situation these days. Within the last two months, one story said her boyfriend Taylor Kinney was shopping for engagement rings ... another said they broke up.

So we have to ask ...