Taylor Swift wants justice -- after a sting operation in Idaho revealed that a little sports bar was totally cheating her out of ... a few dollars a month.

Swift has attached herself to a copyright infringement lawsuit spearheaded by BMI -- the enforcer of music royalties.

According to a lawyer connected to the case, BMI deployed an "agent" to go on a recon mission at The Sports Cellar bar sometime last year, and the agent noticed the bar was playing music -- including Taylor's stuff -- that they hadn't paid for the right to play.

We're told they even used the allegedly stolen music for Karaoke!!!! Have they no shame?!

Swift and co. are suing for unspecified damages -- but compared to the millions she's raking in right now, this thing in Idaho is totally small potatoes.

"Cocaine" is never free ... neither is Taylor Swift, John Fogerty and the Harper Valley P.T.A. -- this according to the secret agents who claim they caught an Idaho sports bar playing music they hadn't paid for.

As TMZ first reported, BMI -- the enforcers of music royalties -- sent a spy to The Sports Cellar bar in Idaho to see if they were playing music they hadn't paid for the rights to use ... and according to court documents, this is what they heard:

-- Cocaine
-- Amarillo By Morning
-- Harper Valley P.T.A.
-- Long As I Can See the Light ... by John Fogerty
-- She Thinks My Tractor's Sexy
-- Here Without You
-- Should've Said No .. by Taylor Swift
-- I Get It
-- Five Dollar Fine
-- Gotta Get Me Down Home

After the recon mission, BMI, Taylor Swift and several recording artists filed a lawsuit against the bar for copyright infringement.

So why would the secret agents for BMI target little podunk bars? Because they're sending a message to every small joint in the county -- Big Brother is always watching.

Now this is funny ....

Gerard Butler in London. Michael Jackson would pee his pants if he saw this.

Before becoming a legendary pop icon, this little girl was just another normal, everyday celebuspawn growing up in Hollywood. Can you guess who she transformed into?

DJ AM had more shoes than freakin' Imelda Marcos -- and now his homies have posted a bunch of his sought after sneakers on Ebay to raise money for the DJ AM Memorial Fund.

The fund -- dedicated to helping people struggling with addiction -- should pull in some serious dough from the auction ... some of these sneaks are already going for more than a thousand bucks!

... or are you just a complete idiot?

Floyd Mayweather and a hundred thousand of his closest friends -- plus Diddy, Ray-J, Mario Lopez and Jermaine Dupri -- hung out at XS in the Encore hotel after the Manny Pacquiao fight.

Common sense eventually prevailed. Floyd put the money away rather than "make it rain."

Chew on this -- sometimes certain sets of teeth go through a crazy, mysterious change after the owner becomes famous!?! Check out the proof!

The little things in life go a long way -- so spot the subtle differences in the following photos!

**HINT -- There are THREE differences in the above picture!**

Some of the biggest models in Hollywood have aged like wine. Others ... not so much.