Hi Kiki,
Do you use iPhoto? If you do, select the picture you want to use.
Go to File, Export
Click on "Scale Images No Larger Than"
Change either the width or height to 300
Then save the file in a folder (where you can find the pictue)
then Ta~da!
You have resized your photo and its ready to share on YT!
If you don't have iPhoto, let me know what software you use for you photos. |