Turn Off Featured Image Function

Help! How can I turn off the featured image function? I feel like it's only double work for me. Is there a way that I can just use the first image on my post as the featured image? Or perhaps a way that the first image on the post or page automatically populates as the featured image? Then if I want to change it I can (although I can't think of one instance where I would need to do that). Thanks! Kim