From a strictly theoretical perspective it would be the inverse square law if the magnet field was generated by a monopole source. However, in reality, magnets are two poles and so the field decay calculation is more complicated and can range to an inverse cubed decay or more depending on where you are in relationship to the composite field and the shape of the field (could be multiple poles - 4, 6, 8, etc).
If there were strong residual magnetic fields, warning signs would probably be in place. Your camera should be fine
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"