GD Watermark Question-
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From: tedd on 19 Sep 2010 11:52 At 7:56 PM -0400 9/17/10, TR Shaw wrote: > >Nevertheless, I say again the key is to add something is that if an >employee of a customer who purchases the image and resells it that >you have a possibility to prove. Yes really smart bad people can >defeat but 1) most of these aren't stealing your pictures and 2) the >others don't know you have embedded a copyright. > >tom While it won't defeat smart bad people, it will cause them to pause: http://webbytedd.com/b/protect-image/ Cheers, tedd -- ------- http://sperling.com/
From: TR Shaw on 19 Sep 2010 12:32 On Sep 19, 2010, at 11:50 AM, tedd wrote: > At 12:36 AM +0100 9/18/10, Ashley Sheridan wrote: >> >> I know this is getting a little off-topic here, but surely the way a >> jpeg destroys data in an image would destroy the stenography information >> too? To the human eye all would appear normal, but the copyright info >> would be lost? >> >> I don't know much about this sort of thing, so I'm making assumptions >> here. > > > It's the difference between lossless and lossy compression. The first meaning no loss in data and the second is loss of data. PNG and jpeg is lossless whereas gif is lossy. Actually GIF is lossless (it uses LZW encoding) PNG is also lossless (Ii uses DEFLATE). The specification for JPEG supports both lossy and lossless. And then, of course there is wavelet used in JPEG2000 and other wavelets These are lossy. Tom
From: tedd on 20 Sep 2010 11:57 At 12:32 PM -0400 9/19/10, TR Shaw wrote: >On Sep 19, 2010, at 11:50 AM, tedd wrote: > >> At 12:36 AM +0100 9/18/10, Ashley Sheridan wrote: >>> >>> I know this is getting a little off-topic here, but surely the way a >>> jpeg destroys data in an image would destroy the stenography information >>> too? To the human eye all would appear normal, but the copyright info >>> would be lost? >>> >>> I don't know much about this sort of thing, so I'm making assumptions >>> here. >> >> >> It's the difference between lossless and lossy compression. The >>first meaning no loss in data and the second is loss of data. PNG >>and jpeg is lossless whereas gif is lossy. > >Actually GIF is lossless (it uses LZW encoding) PNG is also lossless >(Ii uses DEFLATE). The specification for JPEG supports both lossy >and lossless. And then, of course there is wavelet used in JPEG2000 >and other wavelets These are lossy. > >Tom Aahh... I stand corrected. My statement was from my experience of taking images (i.e., jpeg/png) and then creating GIF's from them where the process was lossy. The process took the entire palette of colors provided by jpeg/png and then picked the "best" 256 colors to create the image, which is no question lossy. However, the data compression technique to create the GIF was not lossy. My bad. Cheers, tedd -- ------- http://sperling.com/
From: tedd on 20 Sep 2010 12:12 At 12:21 PM -0400 9/19/10, TR Shaw wrote: >On Sep 19, 2010, at 11:45 AM, tedd wrote: > >> At 6:56 PM -0400 9/17/10, TR Shaw wrote: >>> On Sep 17, 2010, at 6:49 PM, Ashley Sheridan wrote: >>> >>> > At the end of the day, if you want to prevent people downloading your >>>> images, then just don't show them the image. >>> >>> Actually you can. Serve up an image from the DB and add >>>watermark or whatever on the fly for web browsers. If a user >>>downloads (assuming that s/he bought the image or the image is a >>>"freebie" ) the image comes from the DB directly to the user using >>>download headers. >>> >>> Tom >> >> Actually you can't. >> >> Regardless of where the image comes from (DB or file), when the >>user see's the image, they have it. >Tedd, > >You missed what I said: > >orig file on server -> php that addes watermark when image is >required by a browser -> browser accespts and displays image with >watermark on it. Similar to you example. > >Tom Tom: Are you saying that all images shown to the user via a browser will have a watermark on them and if they get permission (i.e., pay for it) then they can have access to a link that will allow them to download the image? Is that what you are saying? If so, then why not say that? Our points have been that browser download images -- period. If you want to protect your images, then you have to come up with a protection scheme other than simply using browsers to view the images. Cheers, tedd -- ------- http://sperling.com/
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