2 Chainz ARRESTED for Weed -- Says Cops Wanted Pics

7:00 AM PT -- OK, This is getting RIDICULOUS ...

We asked the Maryland State Police WHO ASKED to take the photo ... and a rep for the cops told us, "We cannot confirm who initiated that at this time."

Ummm ... how hard would it be to ask the cops???

Interesting Point -- 2 Chainz posted the pic on HIS Twitter page ... meaning it was most likely taken by someone in 2 Chainz's camp ... which would mean the rapper probably initiated the shoot.

Oooooor ... the cops took the pic and sent it to 2 Chainz.

Something's fishy here ...

2 Chainz was arrested for marijuana possession in Maryland last night ... and the rapper is PISSED -- claiming cops were just "f*ckin" with him ... and then asked him for pictures.

The guy behind the hits "Spend It" and "I'm Different" was busted around 10 PM in Easton last night after Maryland State Police pulled over a white van he was traveling in ... along with 6 other people.

But cops say 2 Chainz was in possession of weed -- so he was arrested. He was the only person in the van taken into custody.

2 Chainz was taken to a nearby station where he was booked, released and even took a picture with police ... but the rapper says he only took the shot because THE COPS asked him for it.

After the incident, 2 Chainz went on a Twitter rampage -- saying, "dam police f*ckn wit a n**ga."

He continued, "Locked me up and then Wanted pictures smh (shakin' my head)."

2 Chainz also claimed that he didn't exactly have a bag of weed on him at the time ... only a grinder (a device used to crush up weed so you can smoke it.)

We reached out to cops -- so far, no word back.