python Tkinter Turtle screen background
Per the turtle documentation, bgpic() only accepts GIF files, not JPEG:
turtle.bgpic(picname=None)
Parameters: picname – a string, name of a gif-file or "nopic", or None
Set background image or return name of current backgroundimage. If picname is a filename, set the corresponding image as background. If picname is "nopic", delete background image, if present. If picname is None, return the filename of the current backgroundimage.