Matt Prokop's mug shot has been released ... and the former Disney Channel star looks very concerned after his arrest on child pornography charges.

The Victoria County Sheriff's Office in Texas released the photo Tuesday morning ... with Prokop standing behind a booking board that an officer is holding in front of him.

Prokop's got a bushy beard, his hair is swept to the left ... and his eyes are wide, seemingly with worry.

Sometimes celebs smile in the mugs ... but not Prokop -- the charges he's facing are no laughing matter.

As we told you ... Prokop was arrested Christmas Eve on multiple charges, including alleged possession of child pornography and resisting arrest.

Police took him into custody after he allegedly violated bond conditions of charges filed in 2024 ... possibly connected to when he allegedly assaulted his girlfriend.

Prokop has a long history of trouble with the law ... including as the subject of a restraining order his ex, "Modern Family" star Sarah Hyland, filed against him. He was ordered to stay away from Hyland for three years.