I like to try not to show them the picture.
I would generally prefer for them to use my description of the monster to create their own image. Their minds will fill in details for certain adjectives like imposing, beautiful, grotesque, pustulent, elegant, brutish, sexy, and dreadful. Because it's their minds creating those details, they'll concoct an image that's personal to them and will therefore be more accurate to those descriptiors than I would be.
It's a lot like a horror movie not showing the monster because nothing is scarier to you than what you imagine to be scary.
However, I will show the picture if they really want to see it, or if they feel the description is vague or confusing.