First of all, it's a rather dirty aircraft indeed. On the other hand, I noticed three dust spots: one above the left main door, halfway between the fuselage and the top of the photo, another underneath the marking 'A320-200' also halfway between the fuselage and the bottom of the photo and finally the last one underneath the right engine, also halfway to the bottom of the photo. As stated above, if you add excessive contrast, you will notice many more dust spots, not visible under normal contrast.
The best thing to do is to clone away the visible spotsand reupload the shot. After that, I think it's best to spend some time cleaning your sensor.
[Edited 2005-01-10 20:01:18]
Ivan Coninx - Brussels Aviation Photography