If a grid element is set to "100% tall" (CSS class wb_colalign_full), an image can be inserted that is scaled to the full size of the grid element - like a background image.
The CSS classes
fullsizeimg = vertical alignment centered,
top_fullsizeimg = vertical alignment at the top and
bottom_fullsizeimg = vertical alignment at the bottom
are available in the editor for this purpose.
The file must be entered in /settings/compress.php:
$webutler_compress['css'][] = 'content/style/fullsizeimg.css';