I was wondering the same thing. It is possible but not directly.

You can do it one of  two (2) ways.

Using php or just referring a .jpg or image of your choice.

I prefer the later.

Where you already have a webserver setup creating the .jpg image and your sketch just reads the .jpg file.

You may still have to to merge to two using php.

However once you sign the app its possible.

There is  sketch on openprocessing.org that does this. I will post it when I locate it.

Here is one .. the sketch has to be signed

http://www.openprocessing.org/visuals/?visualID=4112



If you hit the refresh button a few time you can see people move frame to frame

1. PImage x;

   void setup(){

   size(320,240);}

   void draw() {x = loadImage("http://207.251.86.248/cctv5.jpg");

   image(x, 0, 0);

   }

Here is the other one

http://www.openprocessing.org/visuals/?visualID=4147

Inspired by this:

http://www.openprocessing.org/visuals/?visualID=4112

1.   int x = 352;

   int y = 240;

   int numr = 5;

   int numc = 5;

   float sfac = .50;

   void setup(){

   size(int(x*numc*sfac),int(y*numr*sfac));

   }

   void draw() {

   scale(sfac);

   int i = 3;

   for (int r=0;r<numr;r++) {

   for (int c=0;c<numc;c++) {

   String s = String.format("http://207.251.86.248/cctv%d.jpg",i++);

   PImage p = loadImage(s);

   if (p != null) {

   image(p, x*c, y*r);

   }

   }

   }

   }

Yeah, I want that to happen too (remote activation of a webcam using a signed Applet). Looks like it's not possible (yet?).