[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 mcs):

 I do not know enough about NoScript to evaluate the proposed fix.  Kathy
 and I did examine this issue from a canvas fingerprinting perspective.  It
 turns out that Google's JS code does access canvas data; it draws images
 to a canvas and then uses toDataUrl() to pull out the data.
 Unfortunately, Tor Browser blocks access without showing a prompt on pages
 such as the www.codediesel.com demo because of the third party
 relationship.  The following was logged to the Browser Console (very long
 URL truncated for brevity):
   On http://www.codediesel.com/demos/google-recaptcha/: blocked access to
 canvas image data from document
 https://www.google.com/recaptcha/api2/frame?c=03AHJ_VutAFy..., script from
 https://www.gstatic.com/recaptcha/api2/r20150604090638/recaptcha__en.js:268

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16267#comment:3>
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