[tbb-bugs] #16267 [Tor Browser]: NoCaptcha Recaptcha is not working because of canvas fingerprint blocking

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#16267: NoCaptcha Recaptcha is not working because of canvas fingerprint blocking
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     Reporter:  szgal        |      Owner:  tbb-team
         Type:  defect       |     Status:  new
     Priority:  normal       |  Milestone:
    Component:  Tor Browser  |    Version:
   Resolution:               |   Keywords:  tbb-usability-website
Actual Points:               |  Parent ID:
       Points:               |
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Comment (by cypherpunks):

 >it draws images to a canvas and then uses toDataUrl()
 A, yeh, really.

 I thinked a bit and now I know how to fix canvas fingerprinting for
 toDataUrl.

 1 toDataUrl must return not data: URI, but a blob: URI. It won't break
 sites which use this URI to show the image to the user, but it will
 disallow to derive pixel data from it.
 2 It must be only allowed to be used as an URI for image: in CSS, as src
 for IMG, etc. Using it in XHR or anything other than image must be
 disallowed.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16267#comment:5>
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