SU is a 3D package that can use 2D images to dress up a model - although it can be used for 2D tasks, it’s like using a hammer to put in screws (actually, more like using a screwdriver to put in nails… both of which I have done when I can’t put my hands on the right tool immediately; it gets the job done, but not really the best way to do it).
If it’s for a FaceMe component, then simply edit the image in an image editor so that they have a uniform colour background and save it as a PNG file with transparent background. Import it, make it a component and tic the box that says “Face Me”.
If you want a vectorised version, then use a program like CorelDraw to trace it into a vector and export/import it into SU.