I use BMP that I converted from PNG format. But I do not use MSK files. Change the white RGB(255,255,255) that you want to remain as 'white' to RGB(254,254,254) which is slightly not 'white' but VFP will not make this transparent. I do not believe that there is a setting in the image class that allows you to specify the transparent color value -- it is fixed to RGB(255,255,255); possibly someone else knows how to do this.

I found that the PNG format transparency did not always work in VFP as wanted, so I converted to BMP to control this. If there are a lot to convert, then you might try a google search for "bulk change image format PNG to BMP".