change color image (clipart) to greyscale (black&white)

Is there a way to change a color image-graphic-clipart, in my document, to a black and white image?? Let's say it's an image of an red apple and I want it black and white so I can also change the opacity and put it in the background as a watermark?

I know how to change the opacity of a color image and I know how to put an image in the background as a watermark.

I don't want to just print my whole document as greyscale. I might have a mixture of color images and black and white images (clipart basically).

Is there a way to do this in Pages 09? I know I used to do it in MS Word. But, I haven't found a way to do it in Pages. I searched the forums, but did not find any thing.

Thanks!