After completing these tests, we found that an aspect ratio of 9:16 worked best across all devices. We suggest using images that are 640px by 1138px, or 1080px by 1920px if you want a larger version.
When you upload an image above 640px by 1138px and over 100Kb the Skycore platform will transcode and optimize your image and adapt the markup to fit the screen width. Images 640px by 1138px and below may have higher file sizes but will still be transcoded on delivery if required.
When we tested the different devices, we found that the iPhone 5s and iPhone 6 would first open up to a preview screen and then would display a full screen version of the image if you tapped again. In that preview screen, there is a border on both the top and the bottom that cuts off some pixels. We did some research and were able to find the exact number of pixels for the suggested screen sizes that are being cut off for both the iPhone 5s and the iPhone 6. We suggest that when creating your MMS images that you refrain from putting any logos, barcodes or important information in these temporarily covered areas. You can see in the image below the red area that represents the covered area. Due to the popularity of the iPhone 5 and 5s that you keep important information far enough from the bottom and top edge.