Normally, img is an inline-element, which means, that it's being aligned to the baseline of the text of your parent-element. This leaves a nasty space underneath your image.
You can prevent this with
img{
display:[inline-]block; /* or inline-block if the img isn't the only element in your div*/
}
This removes the reserved space underneath the image.
you can change the alignment by
img{
vertical-align: [top|middle|bottom|baseline|...] ;
}
to align it according to your text.
In general, you can only vertical-align inline elements. So an image with display:block
won't be affected by a vertical alignment declaration.