Custom post type help?

Hello WP Folks!

I need some help! I own a website, I am willing to create the easiest posting system for my web, is all about links and automatic generation.

I want to have some kind of custom field that when i put a link to that field and then when I hit “Publish”, the post will generate a image linking that link, like if I have a download image icon and I have the download file URL and I paste it in the field, then when I hit Publish, can it generate a chosen image for that link so it appear on the post.

I don’t know if i’m explaining this well, but I think is understandable.
Thanks.