Plugin to automate adding a watermark?

[Elisant]

I run a website called veryliberating.com and manually edit all images submitted to the site.

In a fashion similar to icanhascheezburger.com, I add a semi-transparent black bar to the bottom of each image, which lists the URL of my site. My question is, can I automate or simplify the process of doing this?

Essentially, what I currently do for each image is...

1) Resize to 450px wide if wider than 450px

2) Paste my 80 x 15px semi-transparent PNG with my site URL as a new layer

3) Manually move this new layer from the top left corner to the bottom right corner

4) Select a portion of the black bar and stretch it to fill the whole image width

* If I start with a 450px wide semi-transparent PNG to get around step 4, then images which are less than 450px wide get widened when adding this new layer and then require cropping to get them back to their original size.

Perhaps there is a plugin available to add a new layer to a different default location, or to more easily add this watermark-like layer to fill the bottom of the selected image?

Any ideas or suggestions are appreciated.

Thanks!

[Simon Brown]

There's EasyWatermark (search for it), but personally I recommend using Libgd (assuming you're using PHP) to fully automate it.