optimizing a simple image blog.

i have an image blog that is formatted like a traditional blog - it is 1 column with no sidebar where each post is an image with about 100 words of text describing it in the body if the post. i have wp set to show 10 posts per archive page. there is a footer menu with 4 pages not related to the blog. i have about 200 posts. i use chris pearson's focus theme. by default it has all tags and category links hidden. if i am trying to rank by image is there any reason to include categories that group my images by subject? i typically have like 5 categories and put them at the top of the blog as a primary menu. is there any good reason to do this - other than tradition? i also have no-indexed everything but posts. is this a bad idea? also should i include a search function for visitors to search for images? thanks for any help - i know nothing about seo - other than the main way to get traffic is to make good content.