Pity no reply as I'm testing this theme as well and encounter the same problem.
Did you solve this by yourself?

Thanks,
Matthijs

Katryne wrote:

Try using GThumb+ plugin.

Thanks for your reply but I rather keep the layout as it is and would like to see it resizes so it fits in the thumbnail space... (to have a black, or other colour, border at left and right side).

I can see what you mean .... and it's indeed close to what I want. But I do not like it's hiding the caption and only if you hover over it it will appear ....

Hello. Edit the file /plugins/GThumb/template/gthumb.css

Adjust to settings below:
}
#thumbnails .gthumb .thumbLegend {
  position:absolute;
  z-index:100;
  bottom:-18px;
  top:auto;
  height:43px;
  left:0;
  right:0;
  padding:5px 0;
  width:100%;
  background:rgba(0,0,0,0.7);
  text-align:center;
  overflow:hidden;
  color:#aaa;
  -webkit-transition:all 200ms ease-out;
  -moz-transition:all 200ms ease-out;
  -ms-transition:all 200ms ease-out;
  -o-transition:all 200ms ease-out;
  transition:all 200ms ease-out;
}

Height and bottom settings.

Best Regards
Robert