My problem is that I have a fixed height layout, and when I open big images, like this, http://www.reinorpg.com/resources/displayimage.php?album=topn&cat=0&pid=7004#top_display_media , It brakes.
It would be nice if this page shows a bigger thumbnail of the image, and if it's has a bigger original size, when you click it, open in a new window.
Can someone help?
Please read the docs. You have to enable the intermediate-sized view and set it accordingly. Additionally, we're still not able to view displayimage.php. Next time please set the permissions accordingly before posting a link, so we can see what you're talking about.