How to transfer one photo from PC to Iphone 6?

I don't want to sync all my photos, I only want one photo from PC on to my phone.

Just email the picture to yourself, its effectively the same.

Plug in your iphone using the usb cable and go into the iphone using the windows explorer DCIM folder (my computer)

Could email it to yourself.

It is easy to do that. You can try iCoolsoft iPhone Transfer for mac. It is easy to use. In addition, it can help you transfer your video, message to you iPhone 6.