Looks like Yahoo! stopped maintaining the image optimization service called smush.it. So people have been asking questions on the mailing list. I don't have any inside information from Yahoo about the service, or whether it will be back up again. But let me try to answer some of the questions.
History: quick refresher
Nicole and I launched this simple tool called smush.it at the Ajax Experience conference, Boston 2008. (Past blogs). It was a quick hack based on a few simple tools documented here and there. The knowledge was out there, I wrote blog posts and spoke at conferences. Instead of yet-another-talk I thought - why not a quick tool with a browser extension, just to prove the concept and show how much people can potentially save. Nicole jumped in and people seemed to dig the tool. A lot.
The initial development version was hosted on imgopt.com (which is still live and you can see how it used to look like initially) and smushit.com and smush.it. Hosted using Dreamhost's shared hosting which handled the initial load surprisingly well, but later on DH saw too much traffic and disabled some of the command line tools required. So imgopt.com no longer works properly.
Good folks at Yahoo took over and generously hosted the free service from 2008 till last week or so.
What's a dev to do now?
Since the smush.it conception a lot of other tools came up. There are probably good free hosted options out there. But most people have moved to using grunt/gulp tasks and do everything in-house. Which is the way it should be.
Quick NPM search reveals this popular package that should get the job done.
UPDATE: thus spake Kornel
— Kornel (@pornelski) April 6, 2015
ImageOptim is probably the best tool out there, but it's not a hosted service. It's a mac app, created by the amazing Kornel. It's drag and drop and highly recommended for designers and all folks that have day-to-day job of dealing with images on the web and don't have the luxury of a build process that does all the image optimization for them
For folks that want to go DIY route, here's a copy of something I wrote on the mailing list earlier today:
If you want to set something up I'd look at ImageOptim's code on github and lift the command-line tools from there. Just the dir listing gives you an idea of the tools you need:
You don't have to use them all, just pick couple PNG (e.g. pngcrush, optipng), one JPEG (e.g. jpegtran) and the only GIF (gifsicle) optimizers and you're 95+% there
More reading and simple command-line examples:
For even more reading and best-of command-line options and flags, dig deeper into ImageOptim's code
Close with a joke
Ajax Experience, Boston, 2008. Quick 5 minute sessions in the morning. All "quick" presenters sitting by the side of the stage. Nicole and I announce smush.it with something like "today we're releasing a tool called smushit". John "jQuery" Resig goes "Erm... what's a Smu?"