Our standard graphics file is a JPG with 70% quality and 640 pixels wide. Using their browser, our memberís select graphics files they are going to upload and then press the UPLOAD NOW button.

QUESTION: What is the best way to do the convert to JPG and/or Resize (if needed) on the client side before transmitting it to the server?

Because we will have a small group and the relationship will be a trusted business-to-business relationship, I can have them download and install and authorize the use of a program.

I can have the program FTP to a specific directory if needed.

I can have the user authorize the use of my code if needed (although I would prefer that they only have to do this once, not for every use).

I want to do my best to prevent attempted hacks against this code to try and use it to transmit files as well.

I need my browser to communicate with the program and trigger it to perform this work, preferably in the background, so that the browser isn't tied up while the upload is taking place.

We are using PHP and open source on the server side mainly. Any help is appreciated.