What methods can be tested to see what was likely the original size?

Question

Without the original image or exif info or knowing who took the photo :)

followup from How to find out the original size of a photo?

Asked by designparadise

Answer

The most accurate, and by far the easiest, method would be to simply ask the person who took the photo.

If you don't think the photo has been cropped, you can try to figure out the class of camera from the aspect ratio (e.g. DSLRs often have a 3:2 aspect ratio and compact cameras often have a 4:3 aspect ratio).

Based on the contents of the picture, you can try to narrow down when the picture was taken, and from that you can narrow down the list of cameras to those that were available at that date (so if a building in the picture was demolished in 2007, the picture couldn't have been taken with a camera released in 2009).

Using clues like the depth of field in the image, you might be able to determine what class of camera was used: an ultra-narrow depth of field might imply an interchangeable-lens camera with a very fast lens.

With information you have about the photographer, you might be able to infer some things about the camera that was used (for example a fisheye image taken by someone on an extremely-limited budget was probably either constructed in post-processing or taken with a fisheye adapter on a cheap camera, rather than a fisheye lens on a full-frame DSLR).

Artifacts in the image may help you determine if or how much the image was post-processed, and whether or not the post-processing will affect the accuracy of the assumptions you are making.

The larger the image is, the more information you'll be able to recover (like trying to guess the sensor size from the image quality). If the image you're working from is very small, just a couple hundred pixels across, you won't have much information left to work from.

Answered by drewbenn

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