Some people, like my twin, still use PCs and we communicate with them. We send them photos and other images and we would like to make sure they can open and view them. Macs have an Edit option that lets you choose to make your images Windows-friendly. To access it select Edit from the menu bar, then choose Attachments > Always Send Windows-Friendly Attachments.
You choose to leave this on all the time, but when it is turned on, images sent to a Mac lose some details like color labels. You do have the option of choosing to use the Windows-friendly attribute on a case by case basis. When you choose the images that will be included in your email, use the attachment icon at the top of the email.
At the bottom of that window is a check box that lets you turn on or off the Windows-friendly action.