The mirror image of the figure is

A mirror image is a reflected duplication of an object that appears almost identical, but is reversed in the direction perpendicular to the mirror surface. (ie left right inversion which means left becomes right and vice versa )

In the given image, the circle is in the top left corner, so the mirror image should have it in the top right. This leaves us with only choices A and D. A, however, is not the mirror image because in A, one of the rectangles, which is perpendicular to the box, becomes angled. 

Hence D is the correct answer.