[cabaalis]

I'll bet that most image requests will be within certain parameters. 2^x by 2^y. So you could probably pre-cache most real-world image sizes, and leave dynamic generation for 1-offs.

[davinic]

AND you could try to figure out how to do that beforehand, but some LRU-type cache solves the problem without any prior knowledge of what those sizes are.

[anamexis]

Well, that's what they're doing.