The iPhone 6 and iPhone 6 Plus screenshots don't accept cropped (without status bar) uploads.
5.5in (iPhone 6 Plus):
1242 × 2208px portrait
4.7in (iPhone 6):
750 × 1334px portrait
4in (iPhone 5 and 5s):
640 × 1096px portrait (without status bar) minimum
640 × 1136px portrait (full screen) maximum
1136 × 600px landscape (without status bar) minimum
1136 × 640px landscape (full screen) minimum
3.5in (iPhone 4 and 4s):
640 × 920px portrait (without status bar) minimum
640 × 960px portrait (full screen) maximum
960 × 600px landscape (without status bar) minimum
960 × 640px landscape (full screen) maximum
