Ok, I apologize, it was a trick question.
There is no
aliasing in the posted image.
It is a sine of 2.04 samples per cycle, which is about 98% of the Nyquist rate, and so definitely below Nyquist.
Here is a center crop of what you get if you apply a high-quality reconstruction filter
to the original image:
The point is that the failure to reconstruct, or reconstruction error, can be mistaken for aliasing, and can even badly affect images that have no aliasing at all.
Just something to keep in mind when comparing cameras, AA filters, and technologies like foveon vs. bayer.
Note to Bart: No need to increase the sampling rate for the diagonals, in this case they already have a sqrt(2) advantage over horizontal and vertical.