Quote - In Photoshop, the image must be saved for the web, and in the separate window, you can designate 15 kb as your final size.  Photoshop does the rest.

BTW, thumbnail size is 15 kb unless that recently changed.

Yup. I have Photoshop CS 3, and I find that for a given quality of jpeg, saving it for the web makes it a little smaller, which is really important for thumbnails. Unfortunately, at least through CS 3 the dialog box doesn't tell you how big the file will be (unlike "save as ..."), so you may find yourself looking at the file properties.

I've also found that, if you are going to crop your picture to make the thumbnail, a good workflow is as follows:

Crop to about 25% larger area than you want covered in the thumbnail.

Resize to 250 pixels by 250 pixels.

Create a new 200 pixel by 200 pixel image.

Copy and paste the cropped image into the new one. It will come in as a new layer, and you can drag it around to get exactly what you want. This has the advangage that it will be exactly 200 pixels on a side.