Even though I'm not on the metro side much why would they make it so you can't change the background without hacking around?
hehehe,,, Tech Support Job Security for when novices try hacking/modding it and break things.
To give Amateur and professional dev's something to do with windows?
The real answer,
MS doesn't really much believe in allowing a lot of things to be changeable in the OS GUI wise for fear of having to support those features, and yes they would have to support them, possibly causing the costs to go up and making Windows that much more expensive, which a lot of people won't pay for and will expect it as free add ons, which is why I suspect that did away with Gadgets (however they realized those were not secure).
Well, considering there are about over 40 different possible combinations of color and patterns on the Start Screen, for many people that will bode fine for them. But for people like us, that only lasts for a month. Of course they should had put in more customization options, but as Windows isn't used just by power users and tweakers but for the large plethora of people that don't really change much to personalize, those current options for the Start Screen are enough.
And this also is a reason towards Microsoft not making a totally feature complete for perfect Windows version at every release. It makes development stagnate as it'll end up like the mac os where the UI doesn't change but feature set does. It also is a marketing move as if you have an OS where you can customize even more than the last, you'll end up wanting to upgrade. Cynical view, yes, but that's that.
Plain and simple, people want to be able to put a custom picture on their displays. They don't want a selection of pre-defined images or color combination choices.
Have we not had the ability to set and change our desktop backgrounds for years? Did Microsoft not introduce the ability to have different wallpapers on each monitor in a dual monitor setup with Windows 8. It seems like the desktop team understood what people wanted, while the Metro UI team just didn't care all that much.
I know that there is a "technical" reason why we cannot just slap an image up there, and it's because of the infinite scrolling to the right that is necessary in the UI. But I'd bet dollars to donuts that some people would opt for a picture of their choosing and then put in time and effort to get everything on 1 screen without having to scroll and in the event they actually needed to scroll..they would deal with their custom picture not looking quite right.
Not to mention the fact that horizontal tiling is a pretty well understood concept (Watch any old Flintstones cartoon for more than 60 seconds and to see how that works)
I think the main issue is that because there are no shadows or borders on the live tiles that they would actually look like a horders bedroom if you had a screen full of them on top of nearly any background that wasn't almost a completely solid and faded into the background. So I'm betting that they wanted to keep it "Beautiful" and not allow people to "mess it up".
Not agreeing with it of course, but that'd be my guess as to the "Metro thought process".
There could also be the reason that putting a custom image on the Start Screen would be pointless as the tiles will end up covering a good 60 percent of the image, and more when you scroll over. I think the new blackberry 10 kind of has this thing too. From a picture I once saw of the home screen, it has these tiles, and after looking at it for a few minutes, it looks like it has a yellow flower as the background in the "grout" of the tiles. You simply couldn't make out what it was. The same concept goes here. The tiles will cover up a lot of the image that if you were to try to make out what the image is, it'd take you a good while and good deal of scrolling left and right or even just going to Semantic View.
A custom image on the Desktop works fine as smaller icons fill it up, even then, when you litter icons, it just looks cluttered and makes the custom wallpaper bleh looking.
Now custom PATTERNS on the Start Screen would be a nicer solution.
I remember having something like this but with a black background with the Developer Preview. There was also another pattern that made the WHOLE Start Screen just tiled top to bottom and in blue, it was pretty neat as the pattern had different shades of blue that just made it all POP out at you.
Use Photoshop or another utility like Paint.NET and take a resource editor like Reshacker or Restorator to imageres.dll
Can you provide some details about which specific resource to change and what image size is best to span the WHOLE screen?
I've been perusing the images.dll and I can tell some of what the image resources are, but don't really know where to go from there.