Problems with displaying large images?
Unfortunately, there are no hard and fast rules when trying to use larger image sizes in conjunction with iOS; it usually comes down to some experimentation.
There is a known issue with trying to load large files on the iPad, which is a native iOS restriction. Newer iPads have a higher limit, but from our internal testing and debugging, the largest image file we've been able to get to load is a 2000px × 2500px .png (roughly 3MB) to load on screen, even if the image file has been downloaded to the device (and throwing no errors). Apple's developer docs recommend not using images larger than 1024 × 1024 (which has since been updated on the newer Retina displays to 2048 x 2048).
We have done some work with large horizontal files before and it usually does require some experimentation. One thing we've found to be key for iOS to render these wider images correctly is saving as 'Progressive' rather than 'Optimized' when exporting for web & device in Photoshop.
After researching supported file sizes, we also found that the iOS browser components that Kiosk Pro is based on downscales larger images to prevent issues relating to memory consumption and stability. This downsizing begins at 2 megapixels for .jpg and 5 megapixels for .png. To translate this into pixels, the maximum possible dimensions for a 4:3 aspect ratio .png that would remain under the 5 megapixel limit is 2640 × 1980.