How do I set a custom thumbnail image when I share my website's link with someone?

[JonsScores]

When I send someone a link to my site, the thumbnail that is shown is a random picture from my site, and it looks weird. I would like to be able to choose the image that is shown with the link. 

Please help.

Thanks!

[JK_Fiber_Art]

Can you post the URL link so we (other volunteer Community Members) can get a better idea of what you're seeing.   For me, when I send someone a link to my site, there's no image as it's just a link and goes directly to my site so it's best to better understand what you or someone else is seeing or should be seeing.