Sync single photos from Mac to iPhone I'm trying so send photos from my Mac onto my iPhone. I don't want to sync whole folders. 

Is it possible to "sync" single selected photos without deleting all the others? Granted, "sync" is the probably the wrong word here. 

I know I can send them via email to my iPhone, but assuming that I have no internet, what else can I do?
Its difficult to give the best answer without knowing which photo manager you use and how often you'd to transfer a photo. For rare transfers, email and Dropbox are good solutions. 

For a more sophisticated approach, I use a smart album in Aperture together with a keyword called "Sync." Now whenever I add the Sync keyword to a photo on my Mac, it is automatically added to the Sync album, which is set (in iTunes) to sync with my iPad.