I think viewing transparent gif image currently in Emacs is fine as it is, since the example image should be used in a light background to view its content. What I meant is about fixing Eww, since I encountered this issue in it. I think at least Eww background should be defaulted to white, not the background color of the current color theme. The default background color for a web browser is also white if no background color is defined in css. It would help in viewing many plain text web pages with transparent images.