Automatically convert links with certain file extensions to image?

Hello all,

I am pretty new to WordPress development, as I have mainly worked in designing and modifying themes. As of now, I am using an “all-inclusive” theme that allows users to post content — similar to Reddit. Although, the purpose of the site is not to have a wide variety of content, but to have a singular topic in which users can post links/images to a board.

As of now, most of the content (that will be) posted includes links to images. How can I make image links automatically display as an image? I have not found any plugins like this, except a text replacement plugin — but that would have to be done individually per post.

I also have another question, how can I automatically replace HTML markup from user-generated posts (basically comments, but seen as a post)? For example, if a user posts,

<a href="www.example.com">Link</a>

or possibly,

<img src="www.example.com/image.png"

it will display the link or image instead of HTML formatting.

Thanks!