Criticize my threaded image downloader
The names Worker and run are very general, while what they are doing is actually very specific (crawl a single web site for images matching a pattern). It would be better if the names reflected their content.
The magic numbers and strings in the code should either be parameters or constants. The thread count, for example, would be a good candidate for a parameter (since you might handle threading differently when importing Worker), while the different parts of the URL could be class constants.
Regarding main, it should IMO only contain that which is necessary for running from a shell (as opposed to importing the functionality in another Python program). That is, when importing everything except main there should be no missing pieces to get the same functionality as when running from a shell.