Embedding photos is a breeze Athena. Right click on the picture you want to embed and click Copy Image location.
Then on the postbox, click the button with the photo icon and it will bring up a popup box where you can paste the address of the image you just copied.
Hit okay and it should show!
While most pics can be embedded, the exception is when another site disallows hotlinking to their photos. In that case you have to download the file to your PC and upload it to a photobucket.com, imgur.com, flickr.com or similar site and get the code for the image and paste it here.
Hope that helps.