The mod uses your $stylevar[cellpadding] and $stylevar[cellspacing] settings. If you have set those to 0 in your style options, that's how it displays. You can change that by editing the the photo_popup code, however. Change the values in line
Code:
<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
to your liking.