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Author Topic: How to [partially] blur screenshots?  (Read 5760 times)

barney

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How to [partially] blur screenshots?
« on: July 20, 2010, 06:00:26 PM »
Folk,

I've seen this many a time, but was never curious 'bout how 'twas done.  Now I need to do it  :o.

You've probably seen screenshots of some app with some or all of the text content blurred, illegible.  Sometimes all of the text, sometimes all but one or two particular lines.

Currently there is a need to do this w/o resorting to GIMP or Paint.Net or the like - I hope!.  Need to take some screenshots of an application that would display information that need not be seen by others, but could display clearly certain elements of the application.  In some cases, I'll need to obscure parts of the text, but leave other parts clear and readable.

There must be some tool to accomplish this, but I wouldn't begin to know how to search for it.  Ideally, this capability would be part of a screen capture application, but a third-party tool would be acceptable as long as it's reasonably fast and simple, i.e. faster than using GIMP :-\.

Example:
  • I want to show toolbar configuration for an email client.  So I want to be able to accentuate the toolbar, but obscure the emails listed in the client screen capture. 
  • Or, I might want to display a page of code with all the code obscured except the code relevant to a discussion/tutorial.
The idea is that only the specific elements under discussion are clearly visible.
Can anyone point to such a tool?  (Recently downloaded Screen Captor:  have not seen that capability available, but have not fully explored its capabilities.)

Deozaan

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Re: How to [partially] blur screenshots?
« Reply #1 on: July 20, 2010, 06:08:31 PM »
Use Mouser's Screenshot Captor.

http://www.donationc...hotcaptor/index.html


app103

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Re: How to [partially] blur screenshots?
« Reply #2 on: July 20, 2010, 06:14:26 PM »
You mean like this?

Screenshot - 7_20_2010 , 7_05_49 PM.png

Mouser's Screenshot Captor does this quite nicely.

Just select a region and use the buttons on the right toolbar:

Screenshot - 7_20_2010 , 7_07_22 PM.png

barney

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Re: How to [partially] blur screenshots?
« Reply #3 on: July 21, 2010, 10:08:11 AM »
Whoops!

Just came back to say that I'd found the blur capabilities of Screenshot Captor, and found two (2) references to it  ;D.

Found it last night, but got so busy playing with it I didn't get back here in time to say, "Never mind, mouser's tool does it."  :Thmbsup:

Thanks, folk.

f0dder

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Re: How to [partially] blur screenshots?
« Reply #4 on: July 25, 2010, 11:09:55 AM »
Keep in mind that you should not use blurring for really sensitive information - while it's not possible to revert the effects of a blur, and attacker can brute-force-blur and get the information he wants.
- carpe noctem

mouser

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Re: How to [partially] blur screenshots?
« Reply #5 on: July 25, 2010, 11:58:49 AM »
there is a different option in screenshot captor for very high security needs; its under SpecialFx->"Secure Black Interlace"

barney

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Re: How to [partially] blur screenshots?
« Reply #6 on: July 25, 2010, 01:58:46 PM »
Yeah,

I found the blackening option, but don't think I'll need it for the proposed project.  Mostly just need to de-focus all except topic/element under discussion.  Looks as though it'll take a while to discover all that Screenshot Capture can do, though  :tellme:  ;D.  So much capability, so little time  :o.

Edit: typos
« Last Edit: July 25, 2010, 02:01:05 PM by barney »

Lashiec

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Re: How to [partially] blur screenshots?
« Reply #7 on: July 27, 2010, 11:08:05 AM »
Keep in mind that you should not use blurring for really sensitive information - while it's not possible to revert the effects of a blur, and attacker can brute-force-blur and get the information he wants.

Pretty interesting. Time to leave blurring behind, then.

wraith808

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Re: How to [partially] blur screenshots?
« Reply #8 on: July 27, 2010, 12:07:42 PM »
Hmmm... what happens if you blur more than once?  And does all software use the same blurring algorithm?  It would seem that the person after the information would need not only the image, but to know the blurring software also.  Is that correct?

mouser

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Re: How to [partially] blur screenshots?
« Reply #9 on: July 27, 2010, 12:23:04 PM »
The more you blur the harder it's going to be to recover..and the blurring is not perfectly invertible, so it's not like they are going to be able to recover the exact image.

However, if you are blurring text (like a serial number for example) then your attacker is not interested in a perfect reconstruction of the original image, they are really just interested in finding the most likely original text string that could be in the source image before the blurring, which is possible.

I don't know what kind of tools there are for this -- i don't think you are going to be able to put the image into some utility and click "go" and have the text recovered -- i think we're talking about a more specialized operation here that would require some expertise.  i'd actually be really interested in hearing from someone who tried to do it.  Obviously you can imagine that in the world of espionage and counter-espionage there has been research on this kind of stuff.
« Last Edit: July 27, 2010, 12:25:37 PM by mouser »

f0dder

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Re: How to [partially] blur screenshots?
« Reply #10 on: July 27, 2010, 02:30:59 PM »
Wraith: you'll need knowledge of the blurring algorithm, font and size, and then you have to write some custom bruteforcing code... it's not guaranteed to work, and most people probably won't ever face such an attack. Still, it worth keeping in mind :)
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barney

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Re: How to [partially] blur screenshots?
« Reply #11 on: July 27, 2010, 02:57:21 PM »
Just curious ... would that fall into the same realm as steganography?  Or is steganography a different beast altogether?

f0dder

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Re: How to [partially] blur screenshots?
« Reply #12 on: July 27, 2010, 03:01:49 PM »
Steganography means hiding data in other data (usually pictures or audio), this doesn't qualify :)
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barney

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Re: How to [partially] blur screenshots?
« Reply #13 on: July 27, 2010, 03:11:16 PM »
'K.  Since I usually see steg* referenced for graphics, just wondered if similar algorithms applied  :-[.  Obviously not  ;D.

rjbull

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Re: How to [partially] blur screenshots?
« Reply #14 on: July 27, 2010, 03:12:11 PM »
if you are blurring text (like a serial number for example) then your attacker is not interested in a perfect reconstruction of the original image, they are really just interested in finding the most likely original text string that could be in the source image before the blurring, which is possible.

Would it help to have an option to first over-write the area to be blurred with a suitably rude message, then blur it?  Just to add a bit more obfuscation?

mouser

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Re: How to [partially] blur screenshots?
« Reply #15 on: July 27, 2010, 03:16:40 PM »
i could add a mode that would randomize the contents of the block before blurring, which would probably make recovering the text near impossible, while still making the blurred region look a bit like the original, which is of course one goal of using blurring.

wraith808

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Re: How to [partially] blur screenshots?
« Reply #16 on: July 27, 2010, 03:18:45 PM »
^ I was just thinking of an option to apply the blurring algorithm more than once, though the idea of some user specified text seems like it would work even better, since it would act sort of like a private key.