gleem

assuming you mean plug your camera in:
Find the "Image Capture" application using spotlight and open it.

Go to the Image Capture Preferences by clicking on "Image Capture" on the top menu bar and selecting "Preferences,"

Select "No application" in the drop-down box next to "When a camera is connected, open."

You have the option to select Apple's iPhoto or another application if you wish.

Quit Image Capture by using the keyboard shortcut Command-Q or going to the top menu bar and selecting "Image Capture" and "Quit Image Capture."

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