Pictures only work from direct links - in other words the pictures already need to exist on the internet, so if you are trying to paste or link something from your own PC, it won't work.
What you need to do is get an account with photobucket http://photobucket.com/ or another image hosting site (you can usually get a free account with these sites), then post your pictures there & then link to them from within you posts here.
Once you have set up an account & uploaded your images, most of these sites have a "share" option for each image, which will give you a number of options for sharing your picture. From there you should be looking for an image link or link code that is formatted as the image address (http:..........) with an image tag (IMG with square brackets around it) at the start & finish of the address, then copy & past the link into your post & voila;
