There are two things to can do to bring file size down.
Firstly image size. These are the physical dimensions of the picture. 400x300 pixels should be small enough to take it below 50k.
The second thing to can do is to alter the image quality, that is the detail or amount of colours in the picture.
tweaking both of these can get you tiny but acceptable quality images for the web....often 15k or less with only a small reduction in quality from a 100k pic