Diners Club and other 85,000 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).
There is a single rectangular shape that is longer then it is wider, and with slightly rounded edges. In the middle of this shape there is a circle, and in the middle of the circle there is a line going through it vertically. Behind the circle there is a darker circle emulating a shadow.