Chage <li>
structure to this
<li><div class="wrapper"><img src="FRONT OPERAH crop.png" width="500" height="400" /></div></li>
& css to this
.pageworkgallery ul{
list-style:none
}
.pageworkgallery ul li{
display:inline-block;
width:50%;
float:left;
}
.pageworkgallery ul li .wrapper{
display:block;
padding:4px;
text-align:center;
}
.pageworkgallery ul li img{
display:inline-block;
width:100%;
height:100%;
max-width:500px;
}