wordpress post-thumbnail crop question. is this even possible?

When I'm using the post thumbnail feature in wp3 and set the thumbnail size to e.g. 230x160 wp crops the image from the top left corner to the set size.

Sometimes this is sadly just the wrong part of the image.

Is there any way to give the backend user the chance to choose the part of the original image开发者_开发知识库 which should be the thumbnail? Like a jQuery script or something?

Right now I'm using a custom field workaround to upload a second image with the excact dimensions...

Any ideas on this?

//EDIT

i just figured out that i was wrong here. the crop function usually takes the middle part of the image (as you can see in the wp-includes/media.php file around line 336). in my case the image didn't even get cropped because (i still need to verify that) my server hasn't the GD library installed.

I am creating a plugin to solve exactly this problem. It's almost done, you can follow the progress on my related question on the WordPress Stack Exchange site.

I think the WP Post Thumbnail plugin is what you want.

Please have a look at this plugin, seems to do exactly what you need: http://wordpress.org/plugins/manual-image-crop/