Bob Dylan didn't just do iconic music in his heyday -- he was painting crap too ... and one of his artwork pieces could be yours ... 'cause it's up for grabs, TMZ has learned.

A painting Bob did in 1968 -- from a previously unseen collection of work from Dylan's Woodstock years -- is on the auction block, and it features an abstract design of a bull ... as well as music notes, bow ties, animals, and other notable imagery.

The painted canvas was given to Woodstock-area resident Sandy LePanto in exchange for an astrology chart ... with the painting remaining with the LePanto family until recently, as it was rediscovered by Anthony LePanto's estate.

The abstract artwork -- which is estimated to be worth at least $100,000 and signed by the legendary singer -- is being auctioned off by RR Auction, with bidding ending on May 23.

The listing notes some minor damage to the painting ... flaking, minor paint losses, etc. ... as the work is unvarnished. Yes, even with a few dings ... it's still going for that amount!

While Dylan may be best known as a singer, he did famously dabble in painting throughout his career ... creating the cover art for The Band's 1968 album, "Music from Big Pink."

Much of Dylan's artwork has not been seen by the public ... which makes this auction item particularly special -- and no doubt, it's a rare item that'll probably fetch a pretty penny.

RR Auction already has a number of bidders ... which isn't surprising -- as a different painting by Dylan and owned by his manager Albert Grossman recently sold for six figures at a separate auction.