Marching ants

The marching ants effect is an animation technique often found in selection tools of computer graphics programs. It helps the user to quickly distinguish an image selection border from the surrounding content by animating the border as a dotted or dashed line, where the segments appear to move in parallel along the border. The consistent movement of the black segments creates an illusion of ants marching in line, from which the name of the effect is derived.

The technique was first widely used by the MacPaint program developed by Bill Atkinson, and has since been adopted by many popular graphics programs like GIMP and Adobe Photoshop. The effect is also known as a marquee selection, as the effect resembles the chaser lights of a marquee sign.