You will need to upload the image using something like Photobucket, Flickr or if you have a website, you can upload the image to that then click on the button on the far left of the second row when you're replying and it will insert
tags. You must get the exact URL to the image like http://i24.photobucket.com/albums/c10/OrcishIncubus/funny-pictures-kittens-cardboard-fo.jpg
... basically how you'll know that you have the exact URL is that it just loads up the image, a webpage with other forms of content don't load (hence the ".jpg" extension at the very end of the URL)
After pressing the Insert Image button, add an "=" after the first "img" ...
copy the URL and paste it after the equal sign. The image should display. Also note that if the image isn't resized, it will automatically resize to fit within the constrains of the forum, so providing an outside link to the image may help.
To help with your problem, what kind of shadowing? Does it look like... well a dark shadow should or does it look like a window replicating itself translucently underneath? It can really go either way, I've experienced artifcating a lot with my current video card, and it's due to it overheating which I don't have much control over right now, and I've experienced seeing windows have a translucent clone underneath at work, which turned out to be something wrong with the monitor. It really varies.