Ganziano | Image Optimizer
You can try our image optimizer here. You can set the unsharp mask filter to much the same parameters as you would in photoshop. You can also set the jpg quality of the picture and see live how it will look so you can get a good balance between quality and filesize.
The nice thing about doing it this way is it always makes the changes from the original master image so you can make adjustments as many times as you like without sacrifising the quality.
Many thanks go to Torstein Hønsi for the serverside unsharp mask function.
This is a working example. Feel free to adjust the levels and experiment with the settings.
original image - 52 K
optimized image - 21 K