Adding Semi Transparent Image as Hover Over Another Image

I want to put a semi transparent image as a hover over another image. Does anyone know how to accomplish this?

See attached image. The left image is with the image over and the right image is without.

Can you share link to your site & page in screenshot? We can check easier.

The site isn't live yet. Still in the process of building. 

You can setup password & share url

Well we are going to be transferring this site over to an existing URL once it is built.

You can share built-in domain (eg: abcxyz.squarespace.com)