In case that your question is "how do I find the direct url to the file" - You don't. I think Newgrounds has specifically made it so that you cannot abuse their services and hotlink to images hosted there.
This simply is to prevent what's referred to as "bandwidth theft". You display images on a remote site, and Newgrounds gets to pay for the bandwidth served, without getting anything back for it.
The way the NG staff has designed it is in a way that still easily shows you the image, with a little bit of NG around it, in order to make it obvious who's actually keeping the file up there.
In short: bandwidth stealing is bad.