The way I do it is in iphoto. I select the picture(s) that I want to post by clicking once on them if I want to select more than hold down the command key while clicking. Then I go to FILE>EXPORT (up at the top of your screen) then a little window will pop up and in the drop down menu where it says SIZE, I click custom and I usually type in 640 then click EXPORT you will need to choose where you want to save them. I made a folder called YT photos. It is very easy to do. I hope this helps!
__________________ Jamie, Mom to Mayzie and Mozes |