Justin Bieber -- Special Delivery ... Here's My Package! (PHOTO)

Justin Bieber seems fed up with the snipers who claim his Calvin Klein ads are Photoshopped where it counts ... so he did what he had to do to make a point.

Biebs posted the photo Wednesday afternoon with the caption, "Photoshop lol" -- but, as we say in the law, res ipsa loquitur ... the thing speaks for itself.

As TMZ first reported, Bieber's legal team threatened to sue a website that claimed to have an un-retouched photo of Biebs' CK ad ... that made him look much, much tinier ... both above and below the Equator. The site quickly pulled it down, but lots of people remained unconvinced.