Wallpapers / Desktop Backgrounds etc..

resizing will always cause problems.

If you are creating them yourself, then create each one individually at the appropriate size. Ie, make the canvas size 1680x1050 for the first one and then create it. Then make a new one with canvas size 1280x800 and create it, etc.

The first two are widescreen and the bottom two are the older 4:3 resolution, which is why it shapes oddly. You'll have to crop out bits or reposition them or something to get it to fit those resolutions.

Not the most high-tech solution but I crop the wallpapers I want using MS Paint.

My laptop display is set to 1280 x 800.
If for example, I found a wallpaper that I wanted to use that was 1280 x 960, I would open using paint and select an area 1280 x 800.
Not perfect if you want to keep the whole image but it stops the image being squashed vertically