In above figure, which constitutes a modified version of the painting Tirets by Francois Morellet, small circles seem to appear and disappear as the eye is moved over them.
Morellet's Tirets Illusion
See also
Moiré PatternExplore with Wolfram|Alpha
References
Seckel, A. The Art of Optical Illusions. Carlton Books, p. 31, 2002.Referenced on Wolfram|Alpha
Morellet's Tirets IllusionCite this as:
Weisstein, Eric W. "Morellet's Tirets Illusion." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/MorelletsTiretsIllusion.html