* small images (< 51 x 51, according to Google)
* medium images
* large images (>= 1024 x 768)
Even if you chose "large images", you still found many images that weren't appropriate for a resolution like 1600 x 1200. Now Google offers a new option: "extra large images" that only includes images for which the product between the width and the height is bigger than a certain number. Google didn't reveal the inferior limit, but it could be around 2,000,000 pixels, so you'll find images that have sizes like: 6016 x 416, 1024 x 2202, 1100 x 3700.
This new option is useful if you're trying to find high-resolution images, but it's still not very good if you're looking for wallpapers that have a certain size in pixels. So how to find a sunset wallpaper for your computer?
* add "wallpaper" to your query. This helps to filter some "noise", but it could also eliminate good results. Example: [sunset wallpaper].
* add "[width] [height]" or "[width] x [height]" to your query. This works because many wallpapers include information about size in the filenames or in a caption. Example: [sunset wallpaper 1600 1200] or [sunset wallpaper "1600 x 1200"].
* restrict the search to JPG images by adding "filetype:jpg" to your query.
You could also try Yahoo Image Search that has a special restriction for wallpaper-sized images, Live Search that lets you find images that have the same size as your screen's resolution or Exalead, the search engine with the most advanced options, including a way to define restrictions for width and height. Flickr also has a group for wallpapers that includes more than 20,000 images: don't forget to sort the images by interestingness.
And if everything else fails, using a Google Search or a custom search engine for wallpapers could be the best way to find a wallpaper.
{ Thank you, Cody. }