Resize Image in Preview

You can resize images in the system application Preview:

• open image in Preview (by double-clicking on image; or find Preview in your applications folder and drag & drop image onto the application)
• click Tools
• choose Adjust Size
• change Width & Height to view in pixels (if necessary)
• change Resolution to 72
• change Width & Height to size you wish

There are other adjustments you can make to photos in Preview - under Tools. 

Crop Image in Preview

We recommend cropping your image before you resize it, if necessary.  You can access the crop tool from view > customize toolbar. Add the crop function

OR

• make sure the row of tools is displayed (click on the toolbox icon - says Show Markup Toolbar when hovering over it)
• click inside image
• drag your cursor to desired crop area (a rectangle marquee tool shows up) 
• click on Crop (crop only shows after you have selected a portion of the image for cropping)

After cropping: