Organizing Images and their thumnails

What's the best-practice method of storing a user's uploaded pictures and it's corresponding thumbnails. I noticed Flickr uses filename distinctions like: http://farm5.static.flickr.com/1234/789456123a_s.jpg where _s.jpg describes the size of the image (_s.jpg = small, _m.jpg = medium...). However, does storing images like the following make sense?

/images/123开发者_JAVA技巧456.jpg /images/small/123456.jpg /images/medium/123456.jpg

...therefore, it's easy to access different sizes by simply pre-pending the folder-size name

Whatever works for you - pick a scheme and stick to it. As long as you're consistent, and document what you do, you should be fine.