Question

For example, in this example, how do I get rid of the spacing between the lines of text (on top of the images)?

Answer 1

Set your line-height on .box_desc. I also adjusted your top value to compensate:

.box_desc {
     position: absolute;
     top: 14px;
     line-height: 10px;
 }

You should tweak the line-height/top values to perfection.

See: http://jsfiddle.net/XhZMv/