on the webassist/plugins/shopping_cart/details.php page, the following code block controls the product image size:
<?php
$imgWidth = 300;
$imgSrc = "../../../" . ($WAGLOBAL_Images_Folder) . ((isset($row_WADAProducts['ProductImage']) && $row_WADAProducts['ProductImage'] != "default-product.png")?$row_WADAProducts['ProductImage']:$row_WADAProducts['ProductThumb']);
$imgSrc = abs2rel(rel2abs($imgSrc,dirname(__FILE__)),dirname($_SERVER['PHP_SELF']));
$WAResultsImage = new WA_Include('scripts/resize_image.php');
require($WAResultsImage->BaseName);
$WAResultsImage->Initialize(true);
?>
<img class="WADAResultThumb" border="0" src="<?php echo(abs2rel(rel2abs($WAResultsImage->Body,dirname($_SERVER['PHP_SELF'])),dirname(__FILE__))); ?>" id="ProductImage" />
you can change the width by editing the $imgWidth variable, or you can add a $imgHeight variable to set the maximum height being used to make the images more uniform.