To Catch A (Twirled) Criminal

You’ve surely seen the news reports here, here and here: a Canadian pedophile was depicted in a bunch of photos online, but they were digitally altered to disguide his identity. German authorities magically restored the photos (almost) and were able to bring the man to justice. I remember watching the TV news when the story broke, and they made a big deal about the photos’ transformation from a swirled mess to a recognizable person. However, anyone who has experience with Photoshop and its filters can restore a photo like this quite easily.

About the Twirl filter

Photoshop achieves the swirled effect with the Twirl filter, available in Filters –> Distort –> Twirl…. As the name implies, the filter twirls the pixels around a center point. I don’t use the filter a whole lot, mostly in conjunction with other filters and other layers if I want some swirling motion. The twirl can be made clockwise or counter-clockwise, which is the key to reversing the effect: simply run the Twirl filter on a previously twirled photo in the opposite direction of the first twirl. The two cancel each other out and you end up with the original image. The reversal does degrade the resulting image somewhat, introducing some blurriness and possibly some artifacts, especially if the photo is in a lossy format such as JPEG (which would surely have been what the authorities were working with in this case.

Let’s try one

Twirled Spidey

Figures 1, 2 and 3: The original photo, the retouched photo, and the restored photo.

Twirled Spidey 2

Figure 4: Restoring a smaller photo does not work as well.

Figure 1 (left) is a mug shot of Spider-Man, which I chose for this example because he’s easily recognizable to everyone and has some details in the face such as the lines and eyehole shapes. Figure 2 (center) is the twirled photo, and to make things easy I’ve twirled the entire photo (you can twirl a selection if you choose) and used the maximum setting. To restore the photo in this case, selecting the entire image and using the maximum twirl setting in the opposite direction returns Figure 3 (right), which you can still recognize easily as Spidey and facial features are restored. One of the keys to retrieving a clear image is to start with the largest original you can find: the smaller the photo, the more pixels Photoshop needs to modify in order to create the twirl and the less data there is to recreate the original, unretouched photo. Figure 4 is the same restoration of the Spidey photo, but it is executed at a smaller size. The pixels on the edge of the twirl were so blurred and warped that Photoshop could not rebuild the original’s features.

Let’s see one of the real ones

Neil

Figure 5: One of the actual pedophile photos. The restored photo is at left, the retouched photo at right.

Figure 5 is an actual photo from the Canadian pedophile case (restored photo at left, original retouched photo at right). There are a few differences between this and the controlled Spidey experiment:

  • Only a portion of the photo is twirled—you can tell because the twirl effect is not reaching all the edges
  • The epicenter of the twirl is not on the center of the photo
  • This photo is from a news website and it’s quite small

The last one is really a killer: I can’t achieve the same results the authorities did because my photo is too small. I’d bet the photos the authorities used were large JPEGs posted on some message board or something. The other two factors—the location and position of the twirl—are not hard to overcome. The twirl’s epicenter is easy to spot—look for the “eye” of the storm—so if you use the Rectangular Marquee Tool, and drag from the center while holding Shift and Opt/Alt you will get a perfect square centered around the center spot. In this case the twirl ends on the left edge of the photo so drag the marquee until it can’t go any farther on the left. Once the selection is made, use the Twirl filter. Some tweaking of the controls may be needed.