Shrink those massive pic files.
Do you have pics you can't use or upload because they are too big? The Preview app on your Mac is a perfect tool to solve this problem!
Resize an Image using "Preview"
"Select Tools" -> "Adjust Size" brings up the Resize dialog box, which allows you to resize any image. (It supports many measurement units, including pixels.) If you want to do many pics at a time, visit the link above, or watch the following video: https://youtu.be/ICvklb1Xmsw