I can't find a way to delete previously imported photos from the iphone in the Photos app (Version 1.0 (209.52.0)). Note that there is a check box to delete picture right after import, but I am looking for a way to delete previously imported pictures without having to reimport them. Typically pictures are automatically imported via iCloud and so when I open the Photos app it does not make sense to reimport them. With iphoto it was possible but apparently not with the new photos app. Someone earlier posted the same question and one solution was given: OS X - How do I remove photos from my iPhone using the Photos app after import?
Nonetheless this doesn't work for me, the delete button is not present in the import page. Most likely this feature disappeared with an upgrade. Moreover when I select images, the Image->Delete photo (translated from the french version) is grayed out.