From the blog:
Omeka 2.3, out today, includes improvements throughout the system, as well as a number of bug fixes.
This release includes improved accessibility, with better labels, skip navigation links, and the addition of ARIA roles and landmarks . We have also added the ability to use PHP’s GD extension for creating file derivatives when uploading. This is in addition to the options to use either PHP’s Imagick extension, or the default external imagemagick. This should allow easier setup on some servers. Read more about configuring thumbnail creation here. Another change is that the drop-down menu in advanced search for “narrow by specific field” now sorts the fields in the same order that you have arranged them, rather than sorting alphabetically, making it easier to find the fields you use most when searching.
Read more: Omeka 2.3 Release – Omeka.