You can currently select from different standard reCaptcha themes in the settings if you don't like the default.
As far as custom theming, I'm not 100% sure the level of effort required to implement that. It might mean changing core files which isn't recommended.
You could probably do just as well with some custom reCaptcha CSS added to your theme.
Also, be aware that the standard width of the reCaptca image is 300px so using it in a sidebar, even with a custom theme may prove to be difficult. You could resize the image, but if you scale it down, it will make it even more difficult to read and more difficult for people to use.
We plan to add more spam protection options in the future, but for now, you might try something like this.
It may be better suited to a form in the sidebar.
Posted 9 years ago on Monday July 26, 2010 | Permalink