Use a USB cable to connect your iPhone to the computer ensuring that the phone is on then copy the photos to your hard drive by using the "Import Photos" choice from the display window on your screen. Select "Properties" after right-clicking the drop down menu and you will see the photo details of each picture. Check out http://www.ehow.com/how_8276077_tell-pictures-were-taken-iphone.html for more information.
There is usually a set of numbers in the "information" about the picture. In the set of numbers there is usually the date. If that makes any sense. I don't know if I even understand what I wrote, but I tried :)