to post a larger photo, I go to a photo album site and upload the photo there.
Then load the photo up in the broswer page and right-click properties of the photo and copy the link. Sometimes you have to remove the mumbo-jumbo from the end of the photo link.
So example, I posted a photo onto
www.flickr.com
http://flickr.com/photos/10693482@N08/2133965435/
I rightclick the photo and the link shows
http://farm3.static.flickr.com/2034/2133965435_272151fe44.jpg?v=0
I then copy that link and click the insert image button in the post and past the link. I delete the tail that is not part of the file path "?v=0"