I've been accomplishing the same by tagging my photos "atomicthumbs photos" or something along those lines.
I would actually love to not have to make personal tags to keep them local for cleaner organization on blog! Or sometimes I could want to use a global tag that I've been using but in one specific instance I want to keep it local, while other times I want them in global tags, without needing to create another personal tag and use them doubly etc. I imagined this could've been helpful if I wanted to link a blog to a non-internety person and not have them confused why I tag with my own name on my own page or whatever
On another hand it could be confusing to cohost users who would except your posts to appear under specific tag, because they've seen you use them, and let's say they bookmark the tag, but they end up never getting the posts. A personal tag would make it clear that they won't get "atomicthumbs photos" if they bookmark "photos" (that could also be accomplished by colorcoding local tags I guess). BUT using personal tags also it makes it possible for them to follow your photos without following the rest of your blog, if that was something they were interested in!
I would also really like this! If I post a tag for, let's say, a specific comic of mine, if someone is viewing my page I'd ideally like them to only be able to view my posts under that tag. Or if I have a general "art" tag, if they're on my page, it'll only show my own art. The work-around would be a unique tag like "[my name] art" but that's hijack-able by other users, so the tag could be filled up with unrelated posts.
I would love for tags to just have a minimum use count before appearing in global search. Counting could be done per post or per user, unsure which is better. Writing short prose in tags is a common practice on Tumblr, where single-use tags don't show up in tag search.