Image Capture: "Please unlock iPhone"

I'm trying to use Image Capture (iMac / OSX 10.9.5) to get some photos from my iPhone 5 (iOS 8.3). The phone is unlocked (in the sense of the screen being unlocked) and Image Capture displays a message "Please unlock <my phone>" and refuses to interact with the device any further. I tried the following things to no avail:

• Rebooted both the phone and the computer
• Entered the passcode in the phone again
• Deleted all files in ~/Library/Preferences related to Image Capture

Any ideas how to work around this bug?