a black square on the center of my first image

i'm a new user of flix and i try demo version when i loaded my avi file and i select vector preset and then on vectorise parameter when i preview the output image i see my first image with a black square in the center of both images (input an output) could somebody explain me why?

That is the watermark in the demo.
You need to purchase a full version.
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jb

ok thank you!