Tkinter error: Couldn't recognize data in image file

I'm trying to put a jpg image to a tkinter canvas. tkinter gives me this error:

couldn't recognize data in image file

I use the code from the documentation:

canv = Canvas(root, width=80, height=80, bg='white')
canv.grid(row=2, column=3)

img = PhotoImage(file="bll.jpg")
canv.create_image(20,20, anchor=NW, image=img)

Same thing with png images. Even tried to put an image into a label widget, but got the same error. What's wrong?

I am using Python 3 on Mac. Python file and image are in the same folder.

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