EXCLUSIVE

The guy who says Josh Duggar used his face on several dating and social media sites -- including Ashley Madison -- is suing the reality star for jacking his image.

Matthew McCarthy says he's been humiliated since Duggar confessed he was addicted to porn and had been trawling for women online. As we first reported ... McCarthy was shocked to see his face as the profile pic on several Duggar accounts.

In the lawsuit, McCarthy says he was raised in a strong-knit Catholic family ... so being connected to Duggar's porn life -- on Twitter, OkCupid and Ashley Madison -- has been mortifying.

He adds he's been getting harassing messages referring to him as "Duggar's boy toy" and "DJ Duggar." He's a DJ and photographer by trade.

Matthew is suing Duggar for the wrongful use of his image, and for damages ... aka cash.