This is plugin from Inigo Media Ltd provides a Template Tag inigo_thumb() that takes a image url hosted within your WP instance and generates a thumbnail for it.
e.g.
<img src="<?php echo inigo_thumb($post['guid']); ?>" alt="example"/>
<?php
$src = inigo_thumb(
$img_path,
$width=168,
$height=null,
$position='centre',
$regenerate=false,
$bg=array(255,255,255);
?>
<img src="<?php echo $src; ?>" alt="example"/>
-
$img_path - The path of the image you want to create a thumbnail from. Assumes the image is in your WordPress instance under /wp-content. The thumbnail is created in /wp-content/[YOUR_ACTIVE_THEME]/images/thumbnails. This can be overridden. Required.
-
$width - The width (in pixels) of the new thumbnail. Default is 168px.
-
$height - The height (in pixels) of the new thumbnail. Default is 168px.
-
$position - The position of the sampled thumbnail within the new thumbnail dimensions. The proportions of the original image are kept. The sampled image can be placed: left, right, top, bottom, centre, tc (top centre), tl (top left), tr (top right), bl (bottom left), br (bottom right). The $position option can be one of: left, right, top, bottom, centre, tc, tl, tr, bl, br. Default is centre.
-
$regenerate - A boolean true/false option to regenerate the thumbnail even if it exists. Useful if you change any of the above parameters. Default is false.
-
$bg - The background colour of the thumbnail, an array of Red, Green, Blue (RGB) values. Default is 255,255,255 (white).