Apple has released new version of iTunes Connect & I got an error message when I tried to set Screenshots on itunes connect for my app.
\"Images can\'t c
Faced same issue, Try using JPG format !! What worked for me here was using a jpg file instead of PNG as jpg files don't use alpha or transparency features. I did it via online image converter or you can also open the image in preview and then File->Export and uncheck alpha as option to save the image and use this image.