how to display content based on uploaded files extention

I am trying to find some way where I can control what content are shown based on uploaded files. For example:
If the uploaded file is a .jpg or .png image, somewhere in the body of the article will display the thumbnail of the uploaded image.

It is kinda like to display file icon based on file extension of file value field. But I don't know how to do it. Can anyone offer a snippet?

Thanks a lot!