Brian, I've got two blogs on the go and one typewriter website that I'm currently putting together and keywords are your best bet for being found by search engines. Typecast images will not turn up in a search, so as tatte mentioned, tags are a common way to make them searchable. Post the image of your typed prose, and then under it include a few keywords that best desribe the content of the typecast. Something else that will help with searches is carefully naming the photo that you're posting. A filename using keywords will help make the typecast more visible.
I wouldn't delete the previous content of your blog. However, if it really has nothing to do with what you're about to post and you want to keep the two seperate, I would start a new blog for the typecast material and leave the old one intact. You might find the urge to continue with it someday in the future and regret having deleted it.
Most important, post a link to your blog here! We'll all be eager to have a look. 