Ever since Facebook upgraded their features, the old way of doing things got covered up. Here's how I do it using Firefox (I hope you're not using Internet Explorer. If you are, you should consider switching to a faster, more stable, and safer browser like Firefox or Chrome):
You start out on the photo page like this:
When you find the image you want, press the "F5" key or just click refresh. After that the same photo should look something like this:
From there, just right-click on the photo and click "View Image":
Now you should be viewing just the file. From here you can copy the URL in the address bar:
And paste that URL where you would normally put your photo address:
I hope this helps!