I clicked on yout jpg file and it looks like your image size is way too big. When this happens to me, I use my photobucket account, using the resize tool, to make it smaller and easier to see in forum mode. Then from photobucket, I do a "save as" and save it back to my computer in a folder I named "resized through photobucket". There is probably a faster way to do this, but this is what I know.
Then in the box where you type your message, at the top, there is a camera icon. Click on that and you can pull the image from your computer.