This should work. I couldn't upload it as the actual background since I am not admin. So you will need to download it and re-upload via ThemeDesigner.
In ThemeDesigner, there should be a "no-split" option. If you uncheck it, the median should reappear. As for placing the seem between the images in the middle, that would require that one of the images be cropped. You would either need to remove from the left/right of the left image or from the top/bottom of the right image. Let me know which you want to do as well as where you want to remove stuff from. For example, if we remove the top/bottom from the right image, do we remove an equal amount from both or remove everything from the top?
The issue regarding to the height just depends on the dimensions of the user's screen. There is no way to get it to fit perfectly for everyone. What you can do it check the "tile" option which should repeat the image vertically so that there isn't any empty background space.
So this is what I came up with (design wise). I switched sides, cropped the right image slightly, and stretched the left one untill they were equal width.
I use a 24 monitor; honestly if I could just get it to fit that I'd be perfectly happy with it. If you need to expand or crop the image in anyway, as long as the "light tower" (City of the Ancients) and the "castle" (Gladstone Keep) are visable that all that really matters. I'd prefer not to use the tile option, I'd rather sacrifice the bottom of the image to fade to black if it comes to that. Also, if you'd like me to credit you with wedpage design on the wiki I'd be more then happy to, it's the least I can do. Thanks.
You can credit me if you want but it isn't necessary. Besides, I am not sure how you would do that for the page background.
Just knowing the "length" of your screen doesn't help. The 24 is measured from one corner to the opposite corner so it doesn't tell us how tall your screen actually is. The best I can do is reduce the image's aspect ration and hope that it fills the height on your screen.
Okay. I uploaded a new version under the same name. It's aspect ratio is 1:1 so, unless a screen is in portrait orientation (which could be for mobile devices), there should be no gap at the bottom.
I'm sorry, I didn't mean to be unclear - my screen height is 12 and length is 21 - I asked somebody about this and they told me to just send the screens diagonal measurments. Also I didn't mean I wanted only the tower and the castle. Oof. Sorry for the confusion.
As you can see from the screen shot, the bottom is filled but the image is largely cut off and the image is very close up and distorted. I feel like you had it closer the first time.
Nevermind, I messed around and managed to get it the way I wanted to myself. Thanks for all your help!