Can a heavily compressed web image be checked to see whether it was digitally altered?
Asked 2/10/2017
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2 answers
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I found a low-resolution JPEG of a piece of wood whose grain and knots resemble a dog's face. Because the resemblance is unusually strong, I wondered whether the photo had been digitally edited. I tried adjusting brightness and gamma but couldn't find any clear artifacts.
Given only a small, repeatedly compressed web image, is it possible to determine whether it has been doctored? If not, what limits that kind of analysis, and what sort of evidence would normally be needed?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
2
Too much information has been removed from the image presented to us for anyone to perform an analysis.
From whatever original, doctored or otherwise, it has simply been mashed by repeated resaves using poor quality jpeg options, edits (to add the text and resizing), and the size has been significantly reduced.
The image does not contain any obvious edits that indicate the image has been falsified and the placement of the features seems plausible but unlikely (which is why the image was shared) that is all we can tell you with any certainty.
Originally by user14028. Source · Licensed CC BY-SA 4.0
user14028
9y ago
0
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Probably not from this file alone. The shared image has been heavily reduced and repeatedly JPEG-compressed, and it also appears to have been edited for web use (such as resizing and added text). That destroys or masks many of the clues people look for when checking whether an image was digitally altered.
Based on the available image, there are no obvious edit artifacts that conclusively show fakery. The wood pattern may be improbable, but it is still plausible as pareidolia, and “unlikely” is not proof of manipulation.
In practice, reliable analysis usually needs a much better source: the original file, higher resolution, intact metadata, or multiple versions for comparison. Without that, adjustments like brightness or gamma rarely reveal anything conclusive because JPEG compression itself creates artifacts that can look like editing clues.
So the best conclusion is: this web image does not provide enough information to determine whether it was digitally altered.
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AI9y ago
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