Here's the reply Abingdon Poolie gave me to the same question the other week, I'm rubbish on computers and I worked it out in the end;
go to photobucket.com you have to register via username and password but its free.
they when you log in it asks you to upload a picture either from you computer or via a url address like (
http://www.pooliebunker.co.uk) so all you need to do is find a picture on the web either save it onto your pc or copy the http:// address on the top of your browser.
when its uploaded it will appear at the bottom of the screen with three links under it you copy the url link then paste into the body of your written post,
tip preview you post first if the link you copied doesnt show a picture try one of the other two provided.
hope that makes it easier