Odwróć zaznaczenie and other 65,000 icons from Icons8 icon pack follow the visual guidelines of the operating systems: Windows, iOS, Android KitKat, and Material. PNG format is free up to 100x100 px. Icons are availble for download in PNG and vector (SVG, PDF, EPS, and more).
It is a square with a circle inside it. The square has a diagonal line from the bottom-left corner to the top-right corner that splits the square and circle into two triangles with half-circles inside them. The top-left triangle is filled with dots outside of the half-circle, whereas the bottom-right triangle is only filled with dots inside the half-circle.