Client Side Conversion of Image Files Before Upload To Server

We want to create a very user-friendly interface that allows people to designate a particular folder of images on their own computer for upload to our server. In spite of the original file size, the uploaded images need to be very small (but with maximum retention of quality).

EXAMPLE:
Original Image = 4200×3000 pixels –
Transferred Image = 210×150 pixels.

The goal is to allow the client to designate the folder of images, then have an applet process each-and-every image in the designated folder down to a predetermined size before uploading to the server.

I’m a newbie, and sure would appreciate some hand-holding on this one.

Thanx So Much – kev