Images are not uploading

So with the following code could some one tell me why my line 21 – comes back as index undefined? Its a simple upload script for uploading images to a custom directory. I believe everything is set correctly, yet when I select an image then hit submit I get an error on that line – saying that image_upload is undefined index. – essentially meaning that the “field is blank” when its not…or wasn’t before I hit submit >_>.

What am I doing wrong?