There should be an image icon in the post editor where you can insert an Image URL.

You need to upload them to a picture website, I use tinypic.com. then once uploaded copy the url it gives you for forums. Then go make a new thread in report section..

When you get to the evidence post, up where you can change the font is what looks like a picture, click that and paste the url into the pop up screen...

There will be things on both ends that loik like this: [ url ] delete those and then submit the thread