This was a simple puzzle, but I did not get as many solutions as I would have expected. Both Suman Saraf and Pratik Poddar sent the right answers, along with three people at home – Karan Sharma (my nephew) and Arushi and Anisha, my 10 and 13 year olds.
The original puzzle BTW is adapted from an optical illusion in Charles H. Paraquin’s Eye Teasers – Optical Illusion Puzzles. It was published in 1978.
Here is the solution, I am taking the liberty of copying the one from Suman Saraf.
Hope you all enjoyed the puzzle!