Moving iPhoto to External HDD

I'm currently moving an iPhoto library from my parents Mac to an external hard drive using the cp command in terminal.

The library is 105GB on the mac, but I have just come back to it to discover the version on the hard drive is 146GB and growing. Why?!?! And when will it stop

I have discovered the problem after checking the folders in the library.

It appears that 'Originals' is a folder instead of being an alias to 'Masters'. Has this happened because I used a terminal command rather than drag and drop from the finder? The reason I did that was because drag and drop was going extremely slow.

Also can I simply delete and link the Originals folder to Masters or is it more complicated than that?

Thank you.