The above image does not have any alternative text. A screen reader would not be able to describe what the image shows.

The linked image of the Jayhawk does not have alternative text. A screen reader would not be able to describe what the image shows or where the link goes.

Above are an empty heading and an empty link. You can't see them except for the space they occupy, but they might be confusing for a blind person using a screen reader.  

This video lacks closed captioning. Without it, a screen reader would not be able to read the content to someone who was blind, and someone who was deaf could not access the audio content.