So if I were to download an image from say reddit or even just online of a fictional character or a real person but no frame of reference. Is there a way I can take the number of pixels that an object takes up and convert that to the objects height? Say for example Demogorgon from D&D or a comic book character.
Obviously I have no frame of reference for the panel or image. So if I were to measure the number of pixels and get say the character is 600 pixels tall. How do I convert that to cm/inches?