This is a simple web-tool which aids in determining the common aspect ratio of an image (eg; 16:9, 4:3, etc), as opposed to a decimal one (1.777 repeating for 16:9, or 1.333 repeating for 4:3)
Simply enter your image's width and height in pixels and read the graph to determine the most likely aspect ratio.
Although I've put effort into making sure this is still a somewhat "advanced" tool, capable of filtering out bad data, I still feel the need to stress that this is tool is not perfect, and could do with a vast amount of polish, which I'll hopefully one day be able to bring.