I have created an application that will automatically resize and screenshot from Defold in the standard sizes demanded by Apple and Google when publishing to their stores. However, I have found that often the screenshots will be black - sometimes running again is enough, but not always.
To do the screenshots I use the windows function PrintWindow, and according to this thread on Stack Overflow (http://stackoverflow.com/questions/1279867/black-pictures-when-making-screenshots-with-printwindow) the cause could be that Defold dows not react to the WM_PRINT message from Windows. Could this be the case, and if so, could you add support for that? If you add the support I will release my application to the public and everybody wins 
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If anyone has some good insights as to how this could be done better or in another way, I am of course all ears.