oké first, sorry for making it into a cynical joke..
plz let me explain, as most pictures are build up from an aspect ratio of 3:2 or 4:3 taken horizontally or vertically most of pbase default stylesheets try to maintain the look and feel of the thumbnail background in order to achieve a more clam appearance.
it is not about adjusting your pictures it is about adjusting your stylesheet
let me try to explain this part for you in the code of your current stylesheet, you can find the lines
TD.thumbnail
{
background-color: black;
padding: 5px;
vertical-align: middle;
width: 200px;
}
where is says width:200px
this means that every tumbnail background will be 200px in width
what you can do is remove this line and play arround with the padding line above in order to achieve the effect you dessire...
in order to change all this you need to copy and paste the code in question into a new stylesheet which you can add in your root gallery.
hope this does help..