Ste Not Work Safe
Joined: 01 Sep 2002 Karma :
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Polarbear Super Spammer
Joined: 24 Feb 2007 Karma :
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Ste Not Work Safe
Joined: 01 Sep 2002 Karma :
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Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
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Posted: 19:25 - 08 Aug 2021 Post subject: |
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<edit> ffs, ste beat me to it, ste for mod!
Polarbear wrote: | For the IT dunderheads here (me ) does that mean the Apple thing only compares the picture's electronic 'title' with the title of known porn images? |
Sort of. A picture, like any other digital information these days, is just a load of numbers. For example an "X" in a simple B&W image might be:
Code: | 10000001
01000010
00100100
00011000
00011000
00100100
01000010
10000001 |
And this is stored in the memory of a computer as:
Code: | 129, 66, 36, 24, 24, 36, 66, 129 |
Now if I wanted to compare this image to another image I could step through all these numbers in turn to see if they're the same but for very large amounts of data that's not a practical use of processing power. Instead it's usual to compare the Hashes.
A hash function is any attempt to capture the essence of the data. For example a simple hash function might be "add all the numbers together and just use the last two digits"
Quote: | 129 + 66 + 36 + 24 + 24 + 36 + 66 + 129 = 510, hash = 10 |
It should be pretty obvious with this example that various combinations of numbers might give the same hash result. This is called a clash or collision and the probability of a hash function generating collisions is an important quality.
The hash function ste mentions is clever in that changes a human is indifferent too - resizing, rotating, colour balance changes - are ignored and so a true signature of the picture is known.
Even so collisions are possible hence the reason a human would need to check flagged pictures manually. ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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