Last year, Macworld posted an update of an old trick from blogger Colin Devroe, which allows you to use your Mac to selectively remove photos from an iPhone or iPad without having to sync the device or download images. To do this, just launch Image Capture.
Image Capture sees your iPhone or iPad as a camera, just like iPhoto does. Unlike iPhoto, though, it doesn't make you import the images to your hard drive before you can delete them. To delete images off your iPhone, either select all of or do command-click to choose the ones you want to remove. Delete by hitting the red "n
