There are plenty of free ways to build an average photoblog, but if you have dreams of creating one that meets your needs and not just the masses, check out Pixelpost 1.7.1. Updated earlier this year with a bunch of new features including an Install Assistant, this MySQL/PHP-based application is a free download and needs only a modicum of technical knowledge and some server space to use.
Everything is tweakable and functionality can be extended with a number of free downloadable add-ons for everything from the ability to use PayPal to let visitors buy photos to adding histograms to images to an Adobe Lightroom exporter. All of them have easy-to-follow instructions for installing them, too.
If you're not the tweaking type, simply pick one of the available templates (also free) and start publishing your photos.