A judge just hammered the guy who stole a piece of Paul Walker's death car ... jailing him for 6 MONTHS.

Jameson Witty and another guy lifted a panel from the T-top roof of the Porsche as a tow truck was transporting the wreckage.  TMZ actually got hold of the video ... which caused prosecutors to charge the 2 men with 3 crimes.

Witty and the other guy copped a plea ... and Thursday was judgment day for him.  The other guy is expected to get the same sentence when he goes before the judge in October.