SilverStripe 2.4.7

Hi

I'm having trouble figuring out something. I am creating an image from a base 64 encoded string and saving it in my assets folder, all working fine, but now I need to create thumbnails (118 x 118) of these images as they are being created. I see that there are several methods in the CMS that allow you to do this but I get an error that no such method exists when I try to apply them to the image.

I'd appreciate any advice.