How do I disable Image Capture (Yosemite) from automatically launching when I plug in my SD card?
First you need to eject your SD card. And then you should plug it back in. Once you do that, the IC will pop up. There is a small icon looks like ejection on the lower left corner (poor design, Apple), click the icon and it will pop out a menu, where you can choose "no application" for your SD card.

Unfortunately you have to do it with every single SD card of yours. Another poor design choice from Apple.