Before the rush

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by evan-pak

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I have an image which I have modified through Picasa ( using Soft Focus - essentially I am making the faces blurred ).

Question is : If I upload that photo to Facebook, and a user downloads it from Facebook, is there any way they can modify the photo so that the face is in focus again?

PS: I am not doing anything mischievous - my subject is against a brick wall holding a Nikon camera, and I just want to focus on the camera strap so I've blurred everything else.

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Hope you don't mind my edit. I don't think this really has anything to do with Facebook. It's more to do with how you've blurred the original (and how much) - and whether it's beyond the point that someone could bring it into enough focus to recognise the subject? – MikeW Feb 24 '13 at 9:18
@MikeW not at all - I have brought it totally out of focus using Soft Focus - so the Camera is below waist line of the subject and every thing else is blurred – user1428716 Feb 24 '13 at 9:20
up vote 5 down vote accepted

There is a technique called deconvolution which can, to some extent, recover distorted or blurred image detail.

Topaz labs have a product called InFocus which uses this sort of technique. It can sharpen certain images, but if you have blurred your faces substantially, I believe it would be beyond the ability of any tool to recover. Maybe on CSI :P

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you meant CSI the TV Show or some tool ? – user1428716 Feb 24 '13 at 9:33
Sorry, meant the TV show, as a joke :) – MikeW Feb 24 '13 at 9:33
ha ha :D .. sorry i dont have any idea on Photo edit software making sure .. I will send it to 24 team too :D – user1428716 Feb 24 '13 at 9:35

If you're doing this for security or privacy, the only sure way is to really mask out the faces with solid color. A sufficient amount of blur will be destructive, to the point where reconstruction techniques like deconvolution won't be effective — but if the image will be subject to scrutiny, it might be hard to judge how much is needed to be safe. Which means that the safe thing to do is use a solid overlay rather than something which is inherently based on the underlying data.

Certainly don't use a filter like mosaic or distortion; it's sometimes amazing how well these can be reversed.

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I work in data security and follow some data security news, images with data hidden by bluring and other image manipulation are "broken" all the time.

Digital filters in software work by taking the image data, doing some math on it and producing the modified image.

Unlike images that are shot out of focus in camera, with digitally blured images we know exactly the math formula the software used - and often we can reverse the formula and get the original image back (sometimes with some quality loss)

I have no idea what Picasa soft focus uses and I don't know if it's reversible, also I'm not going to analyze it, treat this answer as a general warning not as a review of Picasa'a soft focus filter's security

Even if we can't un-blur the image often it's possible to recognize the blured person/object/text/whatever by bluring sections from other images and comparing them (because if we take two similar image and apply the same math to both we get two similar changed images).

So, your bluring method will stop the casual surfer but not anyone who really want to get the data, never use it to hide really sensitive data (especially not text or numbers), be careful and if you want to hide something just paint over it with a solid color (and check it's also hidden in thumbnails, preview images, undo histories and such).

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No, the detail is lost and a JPEG does not contain 'history' to allow the blurring to be undone.

Try it: save an image the the faces blurred as a jpeg, and then re-open it and try to recover the detail.

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wondering if this is possible in Advanced tools like Photoshop ? – user1428716 Feb 24 '13 at 9:23
Hi Tony, you've got some great answers here on Photo SE, but can I remind you that you are not meant to sign your answers/questions with your name, your user card does this for you. – bazite Feb 24 '13 at 16:27
will do, thanks for the reminder and the edits – Tony Feb 24 '13 at 20:09

If the information has been lost the information has been lost, BUT a skilled user could easily enough add in "data" from other face images and reconstruct your image so that it looks like the face belongs.

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