Virtual background on webinar is horribly pixelated (for atendees)

Hi all, 

I'm hosting a webinar later today and just realized the virtual background looks pixelated.

I see it well, but the attendees see it very pixelated and I don't know how to fix it.
- the image measures 1920x1080
- I adjusted in my video settings the HD video
- I also tried with an image twice the size and 1280 by 720 and the same thing happened. On my computer looks fine, but only on mine.

Does anyone know how to fix it? Thanks!