Computer vision is off topic except where it overlaps with computer graphics
Computer vision is in some sense the opposite of computer graphics - going from image to description rather than from description to image. However, despite this intuitive difference, computer vision contains many aspects of computer graphics, and computer graphics often requires techniques which overlap with computer vision. The line between the two will therefore always be blurred.
There will be many questions for which is it is clear that they are not about computer graphics. I believe that the numberplate recognition question is one of these, and I have voted to close it as off topic.
Although recognition questions are off topic, questions about construction of a model based on measured data such as photographs or laser scans are in some cases on topic, and are an important part of work and research in computer graphics.
It is hard to intuitively describe the difference, in order to guide people who are considering voting to close. What might help is to think of recognition as a categorisation problem rather than a construction problem.
This certainly won't provide a clear outcome for all the grey area questions, which is why we need human close voters rather than an algorithm or a strict rule.