I collect images of mitochondria and would like to share them with the rest of the world. As you can see for yourself, it is an enormous variety and there is nothing that even remotely looks like a bacterium in these pictures. The classical picture of the circular mitochondrion is in reality often just a cross section of a long tubular structure. From the pictures below, I think it is safe to say that mitochondria form reticular rather than spherical structures. When you compare them to real bacteria inside eukaryotic cells, you will see the difference as well.