You can use Google Images to find pictures of a particular size (or resolution) using the undocumented imagesize search operator.
Google Images previously offered a useful “search by size” option to help you find images by their exact size (or resolution).
For instance, you could limit your search for landscape photographs to image files that were at least 10 Megapixels in size. Or, if you are were using Google Image search to find wallpapers for the desktop, you could specify the image resolution as 1920×1080 pixels and Google would only return large images with those exact dimensions.
The “exact size” search option is missing in the new Google Images but you can still limit your searches to a particular size by using the “imagesize” search operator in the query itself (see the above screenshot).
Enter the search terms as before and then add IMAGESIZE:WIDTHxHEIGHT to the query. Once you hit Enter, Google Images will remove the operator from the query but the results will only display images that match the specified size.
The search by size operators works on the mobile version of Google as well.