I know this is a really late reply, but the easiest way is to search "whatever transparent", or "whatever png" which will get you an image that someone has already turned into acutout. Then just use any image editor to paste the cutout onto the screengrab.
Worf: She pretty much just sits there out of uniform making shit up and talking about her feelings. Oh you mean this little button not your little one, I don't know ejects the warp core or something.