What solution for thumbnail / image size variation generation?

[eluser]Vi.[/eluser]
I am using on-the-fly thumbnails with defined maximum size.
Mat-Moo's suggestion is what you need but It takes a bit time to complete. Because, after updating picture, content etc. , old picture can be displayed again.

Solution #2 good for small project/web site but for big project/web site you can use Mat-Moo's solution.