Hi handoyo, thanks for replying but I am referring to masking using the alpha channel of a .png file, which is different from using rgba to affect the opacity of the image as a whole. Plus with css I am only aware of the webkit solution which doesn't work with all browsers.
The e-commerce software I was previously using had a global toggle whereby if a .png file was being used, its alpha channel would be applied. I think I mistakenly assumed this would always be the case with .png, and am now looking to find out where I can use this in AbanteCart.
For example this works in AbanteCart with the store logo, but not catalog catagories images.