That white that you’re seeing is actually the background for the content. You can still see it because of the padding thats still there. So to fix this, you’ll need to remove the padding, the background, and maybe the box-shadow as well in order to show the image by itself.
First add background: none; and change the box shadow to none – “#content .portfolio” around line 1722 in your css like this –
#content .portfolio {
box-shadow: none;
-moz-box-shadow: none;
-webkit-box-shadow: none;
background: none;
float: left;
margin: 0 2% 40px 0 !important;
overflow: hidden;
padding: 0;
width: 23%;
}
Next, remove the padding for the entry-content like this –
.portfolio .entry-content {
padding: 0;
}