The code that you have tried looks correct to me, but the img tag will still need to be closed. There is one thing that I can see that might be causing you problems, where the column is being referenced you are using double quotes, you should try using single quotes like this:
<img class="WADAResultThumb" border="0" src="/images/products/<?php echo $row_WADAproducts['ProductThumb']; ?>" />
The way that php works is that the code in the php brackets is processed before the page is sent to the browser. So if you hand code a path like this and the value you are using points to a valid image in that directory it should show up.
When you have the path setup like this what do you see when you test this page out and view the source? Please give this a try and view the source to see what is setup for the image src attribute. If what you see here does not match the path and image name exactly it will now show. You may want to try altering the path just slightly so that it is a relative path to the images folder rather than a site path.