You need to deal with this in Image Capture.
Insert a card and open Image Capture. Without a card inserted you will not be able to make the necessary change. At the bottom left of the sidebar is a little arrow icon. Click on this and you will get a dialog saying "Connecting this camera opens:" with a drop down menu. This probably shows Photos. Select No Application. Exit Image Capture and Photos and eject the card. Then reinsert the card. Normal behaviour should be restored.
