most people want to get rid of mold from photo. I want to add it (image of it anyway)

Hi there,

I want to add an image of mold growing, over a pdf image.  I've got lots of choices of mold growing that I can get from Shutterstock, but they all show mold growing against/on a background.  I want to see the mold, so I can see the content of my image below (photos, graphics, text).

I know how to use Photoshop to remove a background I don't want around a simple shape, but mold growing is anything but a simple shape.

Does anyone here know of a transparent image of mold growing (a .png, with no background) that I can purchase?

Or... is there a way to take an image of mold growing that I can buy from Shutterstock, and get rid of the white (that's the most common) background?

Thanks,

Malcolm