Wordpress is very mature blogging software with several themes available which are geared to photography. You may also like to look at
Pixelpost which is a photography-specific blogging application, free/open-source, etc.
It really depends on what you want to do with your blog, and if you want to do more than blogging, etc. Wordpress is an excellent blogging CMS (Content Management System), but is not terribly easy to build your own themes for it. Luckily, there are a zillion themes available for WP to make it easier. One can then personalize a theme with a little CSS tweaking, some (X)HTML, etc., but many run WP sites with a full canned theme because there are so many from which to choose. There are free themes and themes available for purchase for a reasonable fee.
ExpressionEngine is a more powerful CMS, but it also requires more hands-on involvement. There are themes available, but a mere fraction of what are available for WP. I use ExpressionEngine and like it very much, but it's a more involved commitment with regard to coding than is WP. I believe that most use ExpressionEngine (EE) as a "blank slate" for a starting point. EE easily accommodates multiple blogs, or sections which may or may not be blogs, galleries, forums, etc. EE has many features that WP does not, but WP has some very nice features absent in EE as well.
I did use PixelPost for a few years. It's well geared to projects such as a photo-a-day, and other sorts of linear blogging projects.
Of course, one can run combinations of different packages if needed. e.g. a WP blog with a photo gallery separately, etc. It really depends on what you want to accomplish now, and where you want to take it in the future... and of course, how involved you want to be with regard to the development of your site.