How a photo or document is checked, its modified with image processing softwares.
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This isn’t always an easy task and there are several giveaways to something like this.
For photos this can work through:
Metadata: information the picture contains can be an indicator that it’s been modified
Pixel error rate: Image pixels have a kind of error rate due to compression that looks like noise when passed through specialized software, this error rate can look different in different parts of the image, hinting at being altered through software.
Visuals:
A lot of modifications can be spotted by looking at the image, differently blurred edges, warped parts, incorrect colors, artifacts.
It’s not always easy to spot altered images, however neither is making images look 100% authentical.
It’s easy if you are comparing an original with a new one. You run the original and new one through a hash algorithm and compare the hashes. Even just a one-byte difference in a 4 GB video file will produce a different hash. I’ll explain hashes more if you want.
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