Howdy!
First of all, you need to have the pics on an online host, such as Flickr, Photobucket, etc.. from there you can copy the URL of the pic and use the "IMAGE" button to paste the URL into.. this can be repeated as many times as you want on a post. The downside is that the pics are not permanently added to your post.. if the source changes, the link is broken.
I put em on Picasa,make a collage and then open it in paint,go to stretch/skew to reduce the size then save to my desktop.When you click upload at the bottom of the post it will browse for em an make sure you click embed in post too.