When I tried to update the screenshots for my apps in Apple App Store, I get some message as following :
Screenshots must be in the JPG or PNG format, and in the RGB color space. App previews must be in the M4V, MP4, or MOV format and can’t exceed 500 MB.
and when the size is not correct, it simply reports the error, reject the image file and never say a word about which size it is expected, and I have to figure it out myself.
IOS App iTunes Connect Screenshots Requirement
Format : JPG, PNG (GIF is not included here)
Color Space : RGB (red, green blue)
|3.5 Inch||iPhone & iPhone 3||640 x 960 px|
|4 Inch||iPhone 4+5||640 x 1136 px|
|4.7 Inch||iPhone 6||750 x 1334 px|
|5.5 Inch||iPhone 6 Plus||1242 x 2208 px|
|9.7 + 7.9 Inch||iPad||2048 x 1536 px|
|12.9 Inch||iPad Pro||2732 x 2048|
Reference is here : https://developer.apple.com/library/ios/documentation/LanguagesUtilities/Conceptual/iTunesConnect_Guide/Appendices/Properties.html