When you plug in your iPhone, iPad, or digital camera it can be annoying for Image Capture.app to open automatically in OS X. Luckily, preventing it is easy!
In Image Capture click the triangle/square icon in the bottom left corner. Then click the drop down which probably has Image Capture listed as the default application. Select the top option, "No application". You can also use this tip to prevent any default application from opening (iPhone, Aperture, etc) - do a spotlight search for Image Capture to open it up then follow the same instructions.