There is a recent addition to the Blocks Editor that lets you drag Downloaded Blocks Image files into the the Blocks Editor workspace. (The .png files hold hidden text.)
This only works for individually downloaded images that have not been hand editted.
Watch this little video for when the Blocks Workspace turns green as a .png file is dragged into it.

P.S. Note how the cube_root_test image did not make it into the workspace, because I ruined its draggability by clipping it in MS Paint to show a Do It result.