Easy enough, you don't need any special software either, just use paint on your machine.

Simply open the image, zoom in on the plate, use the 'dropper' function (looks like a little pipette) to match the plate colour then just use the airbrush function or something to go over the plate. job done.

In PB when you upload pictures there is a little drop down menu near the top in the center to say how many photo's to upload in one go (think the max is 20 odd) but remember it'll take a little longer to get them all uploaded