After doing some testing with the Facebook Developer Sharing Debugger (Facebook Open Graph Validator) and checking the specification on the Open Graph website, I settled on the following as my standard open graph meta tags.
// 1x1 Ratio
<meta property="og:image" content="image-1x1.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="1200">
// 4x3 Ratio
<meta property="og:image" content="image-4x3.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="900">
// 1.91 x 1 Ratio
<meta property="og:image" content="image-191x1.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="630">
// 16 x 9 Ratio
<meta property="og:image" content="image-16x9.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="675">
This should cover all current image formats used by social media sites and search engines with only one minor exception. LinkedIn uses a 1.91x1 image with 1200px by 627px dimensions.
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