Apple mac:

• Click on the picture with your mouse so its highlighted
• Press the cmd key and the letter i at the same time
• A new window will open with info about your photo
• Look under kind for the type of photo and size to check the image size is over 100kb
  

PC:

• Right click on the picture once with your mouse
• Choose Properties.
• The "Size" line on the Properties tab shows the image's file size - check if over 100kb