If you have a great camera and you took a great photo* there is really no way to show the resolution of that photo in the internet. Now, you may wanna ask why would you even wanna show off the resolution of such a photo, and I can think of several reasons. Potential buyers may be interested, or maybe you are showing how good a lens is, or maybe you just want to tell people that if they throw gum on a bridge they will get caught.
There is a simple trick that involves a bit of masking and resizing to create a “Magnifying glass” lime you see in the photo above. Hit the jump for the full tutorial (and a few random photoshop tips)