Add "display: block" to image CSS.
IMG is display:inline by default, so you are getting a line of text that contains only image, and a div below it. The line of text has ascent that equals the height of the image and descent that equals descent of current font (which comes from the space between the image and the div). In strict mode, you will get descent even without the space.
So, another way to get rid of the gap is to set the descent to zero by specifying line-height:0 (on the parent element).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…