Same issue I came across, I'm sure it's a quick-and-dirty solution but it worked for me.
- Open your application/library/Grocery_CRUD.php
- Download timthumb from here
- Place timthumb.php in Root directory (in same directory level cache folder should be there)
- Find function change_list_value
Find around line number 333 in Grocery_CRUD.php
$file_url_anchor .= 'class="image-thumbnail">';
Replace with... following
$file_url_anchor .= ' class="image-thumbnail"><img src="' . base_url('timthumb.php') . '?src=' . $file_url . '&w=100&h=100&zc=3' .'" height="50px">';
- Again Find function get_upload_file_input
Find around line number 2545 in Grocery_CRUD.php
$input .= $is_image ? " $image_class'>" : "' target='_blank'>$value";
Replace with following
$input .= $is_image ? " $image_class'><img src='".base_url('timthumb.php') . '?src=' . $file_url . '&w=100&h=100&zc=3'."' height='50px'>" : "' target='_blank'>$value";
Hope this would help you to get rid of ugly size in your list as well as add/edit forms