There are a few ways to implement a picture gallery depending on your needs
1) Use the Multimedia Box rotator
2) WordPress Plugins for slideshows with clickable pictures (D13slideshow and Featured Content plugins)
3) WordPress Plugin for Image Galleries (NextGEN plugin)
Thesis Multimedia Box Image Rotator
If you want to just cycle some images that are not related to a specific post then use the Multimedia Box, the box at the top of the sidebar on the right hand side. All we need to do is upload the images to the custom/rotator folder.
If you want to to have a sequence of images which are clickable, and the click takes the reader through to a specific post then use a slideshow plugin. There are a couple of WordPress plugins for creating a slideshow – please take a look at one of our clients slideshows at Ronald Rae Hand Carved Granite Sculpture: this has a slideshow on the home page and on some other pages: Sculptures For Sale, Sculptures in exhibitions, etc . Each image is clickable and points at a post for an individual sculpture. The plugin is called D13slideshow. You can have as many slideshows as you like on the site.
There is another slideshow plugin called Featured Content Gallery which is similar. but does seem to limit you to one slideshow per site, typically on the home page, or in the sidebar or header on every page
WordPress Plugin for Image Galleries
If you want to display an image gallery within a single post where the images do not link to other posts then NextGEN gallery would be of use. You can have as many image galleries as you like on your site.