I was looking for a public domain picture that would make a good ELA example when I came across "Oriental Dancer Smiling" by Petr Kratochvil.
According to the web site, this picture was captured with a Canon EOS 50D.
Canon EOS 50D
Focal length of the lens:
There is no mention that this picture was touched up. But what exactly was done to it? To answer that question, let's apply Error Level Analysis (ELA).
ELA shows the amount of difference that occurs during a JPEG resave. More white means more change, and black indicates no change.
A real, camera-original picture, should have a lot of white, almost like noise, over the entire picture. As the picture is repeatedly resaved (not copied, but actually loaded into a program and saved again as a JPEG), high frequencies and fine details are removed. With each resave, more frequencies/details are lost until the picture cannot get any worse (returning a black ELA picture).
In this picture, the background is completely black, but the person is not. That means that the background is at a different quality level compared to the rest of the picture; the background was digitally modified. In this case, it was enhanced to make the white look brighter.
With ELA, all edges should be at about the same error level. Similar surfaces should all have similar error levels, similar coloring should have similar error levels, similar patterns, etc. But that isn't the case here. For example, her red headdress has a different intensity compared to the back of her dress, and she has one red strap that is much brighter than anything else. Even the red dangles from the hat are much brighter than the hat itself. The hat dangles appear brighter than the armband (photo lower left). Interestingly, the red bead in her hair (middle of her back) has a much lower ELA value.
Based on this, we can tell that the red in the hat was brightened, the dangles and one strap were reworked, and the original red color was probably darker -- like the red bead seen in the middle of her back.
Mouseover to toggle between the image and the ELA.
We can also tell that her eyelashes were touched up. For example, her faint lower eyelashes cast a very strong ELA value -- stronger than the edges of her nose and lips. And the lines of her cheeks have just as much contrast as her lower eyelashes, but they have no noticeable ELA variation. This means that her eyelashes were enhanced, while her cheeks were not. (Well, not significantly.)
For bonus points, look at the bright ELA spots in the middle of her eyes. Is that a brightened specular reflection, or were her eyes originally looking in a different direction? We know that her eyes were touched up because we can observe that the sclera (whites of her eyes) contains no red veins. (All eyes have veins, and at this resolution they should be visible.) The veins were removed when the eyes were enhanced.
There may have been other changes made to this picture, but these are the things that ELA can readily identify.
End of the Rainbow
The final item that we can tell from this picture comes from the faint blue and red patches. For example, her left arm (photo left-bottom corner) has a faint blue patch. There is a red patch on her back near her right armpit (lower-right corner). In fact, her face has many small blue patches and only a few small red patches.
The red/blue patches are rainbowing. They are a tell-tail sign that an Adobe product was used on this picture. This is confirmed from the metadata: this picture was last saved with Adobe Photoshop 'Save-for-Web' (and not 'Save As') and the user selected a quality level of 60%.
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