Yeah, I think the only way to do this in Corona is via a screen capture using display.save(), which unfortunately does lower the resolution of the image to fit within OpenGL’s max texture size limit. If I remember right, modern iOS devices are typically at least 4096x4096. However, Android devices are typically 2048x2048. This is mostly based on my personal experience.
When I create an app project with CL I start it as 320x480. So will that be the resolution of the image if I use the full screen? Or is there a more standard starting size I should set the app to so I get more resolution?
If you use Corona’s “dynamic content scaling” feature, then images loaded via display.newImage() will be scaled up to the resolution of the device. So, if you’ve set up a content width and height of 320x480, then you should set the pixel width and height of your image relative to the 320x480 dimensions.
You can also create multiple resolutions of your one image and Corona will dynamically select the closest match based on the resolution of the screen if you use our display.newImageRect() function. Details of this can be found here…
http://docs.coronalabs.com/guide/basics/configSettings/index.html#dynamic-image-selection
Regarding screen captures, a captured object will always be relative to the resolution of the device. For example, the pixel width and height of your captured object will be larger on an retina display compared to a non-retina display. This means the capture image size will vary on different devices having different resolution. This is especially noticeable on Android devices. But in this case, I think this is what you really want because odds are a high resolution device also has a larger OpenGL max texture size.