If you're on a computer right click the image and go "Copy Image URL".

Then in the reply options you'll see a section called "Instant UBB Code". Top right is "Image", click that then hit paste for your image URL in this (dont double up on the HTTP though!)

It'll look like this (but without the space between [image] and http):

[image] http://i741.photobucket.com/albums/xx52/P57H/M93%20Stalking%20Rifle/SR931.jpg[/image]

Nice rifle, by the way!