I store images and photos on photobucket
http://photobucket.com/ You click can on a code for forums, (there is a list) that is by the side of the image or pic you have chosen and copy to insert image on your forum post
Click on "insert image" and paste code in the middle brackets - click preview to check the image has worked.
Once you have got the hang of it its easy.
Or you can do what cubagirl does and right click on any image on the on the web scroll down the "Properties" (URL) copy the it if it is a JPEG image, high light and copy URL address and click on MM "Insert Image" and paste, if that does not work try just pasting the address into your message post.