I can't reproduce Apple's first tip on their iPhone tips and tricks page. When they say tap multiple images I assumed them mean tap the 'Select' button in the upper right then select photos one by one but their screenshot shows photos selected while not in selection mode. The only way this screenshot makes sense to me is if they photoshopped the nav bar with the rest of the screen while in selection mode. Am I missing something?
Indeed, the screenshot does appear to have been edited.
The correct way to select multiple photos is to press the Select button, then tap the pictures.
As far as I know, it is impossible to select images without pressing the Select button, and pressing the button changes it to a Cancel button, and the navigation bar title changes to Select Items (or the number of items selected), as well as removing the back navigation button.
On the left: Apple's screenshot; On the right: how it should appear when selecting multiple pictures.
Though I don't have my iPhone on me, here's what I found on my iPad.
If you go to an existing Photo Stream and tap the '+' button, it will bring you to moments. You can tap "Select" for all or just individual moments. From there, you are able to select and deselect one photo at a time!