If you are using Mac OS X Yosemite, you'll have to do another step. I followed these steps but it did not prevent Yosemite from opening iPhoto. Here is a link to preventing this from happening in Yosemite. (***Note: The following link is INCORRECTLY labeled as a duplicate of the question posted here.)

Disable iPhoto auto launch when connecting an iPhone or iPad

If you are using Mac OS X Yosemite, you'll have to do another step. I followed these steps but it did not prevent Yosemite from opening iPhoto. Here is a link to preventing just the iPhoto launch from happening in Yosemite.

Disable iPhoto auto launch when connecting an iPhone or iPad