Google and Bing have search feature that allows users to search images by size. We can use this feature to list only wallpapers when doing a photo search.
Search Wallpapers in Google.
Access Google Image Search webpage by typing images.google.com in the browser address bar. If you are looking for iPhone 4S wallpaper then type the search text as “imagesize:1024×768 iPhone 4S“. This would display the photos of size 1024×768 and which are related with iPhone 4S.
Search Wallpapers in Bing
In case of Bing search engine, access bing image search by typing images.bing.com in the browser address bar. Then type iPhone 4S in the search text box and in the search result page, click the size option and select Wallpaper from the list of available option.
Now the bing search result will display wallpaper that are related with the search term iPhone 4S.