Apple - Maintaining Aspect Ratio while Image Cropping using Preview

In Photo (not iPhoto) click Edit

then Crop

then Aspect, and finally Original

.

As of this writing (August 2016), there is no way to do this using Preview or any other stock program in El Capitan. Photo is nearly stock though, and it's easy enough using Photo.

Do it in iPhoto.

• Open a file.
• Choose Edit.
• Choose Crop or type c
• Check constrain box for Original, the second dimension
• Crop and hit Enter.
• Save.