There are several services that can generate thumbnails like that, but most of them place watermarks on the images or place limits on how many API calls you can make in a month. (Amazon used to offer a paid service, but it was discontinued a year or two ago.)

To my surprise, when I was submitting an article to WPVote recently, I found that the thumbnails were served up by a subdomain of WordPress.com. I thought something along the lines of “Eh? I didn’t know they offered a screenshot service…” and continued about my business.

A couple days later, I spotted Ben’s blog post in my feed reader. In it he explained how he discovered a dynamic URL that Automattic uses, in places like the WordPress.org commercial themes page, to display thumbnails. He posted an email to Matt Mullenweg about it and got this as a response:

You can use it and link to it, but it’s not official. It’s not worth the effort to try to make it into a business – we have to support it anyway for our own apps.

Sounds good to me. Obviously it wouldn’t be nice to use it for something huge and high-traffic, but it seems like they don’t object to us smaller WordPress fanatics making use of it.

http://s.wordpress.com/mshots/v1/http%3A%2F%2Fprothemedesign.com%2F?w=250

There’s now a WordPress plugin that makes it easy to use the thumbnails in blog posts, with a shortcode, or elsewhere with a template tag.

Skitch is great for taking a quick screenshot and resizing it quickly. You can press a keyboard shortcut to take a shot of the entire screen or a selection. You can then crop and resize the image by dragging parts of the window border, then save it to your hard disk or a remote server (perhaps your blog’s uploads folder?). You can also annotate the image with text and arrows, add a drop shadow to the resulting image, etc.

I find Skitch useful for blogging especially, since I often snap screenshots for posts. I also use it to resize existing images when it’s too much bother to launch Photoshop.

If you have a Mac, it’s definitely worth checking out this free application. There isn’t a version for Windows, though I would like it if the folks at Plasq Software would write one.