Apple

Screenshots

5.8" Display - 5 screenshots

1125 x 2436 pixels for portrait
2436 x 1125 pixels for landscape

5.5" Display - 5 screenshots

1242 x 2208 pixels for portrait
2208 x 1242 pixels for landscape

12.9" Display - 5 screenshots

2048 x 2732 pixels for portrait
2732 x 2048 pixels for landscape

Android

Screenshots

JPEG or 24-bit PNG (no alpha). Min length for any side: 320px. Max length for any side: 3840px.

Phone - 5 Screenshots

we can use the iOS 5.5 screenshots here

7" Tablet - 5 Screenshots

1024 x 600

10" Tablet - 5 Screenshots

1920 x 1200

Promo Graphics

1024 x 500 - Feature Graphic
180 x 120 - Promo Graphic

Amazon

Screenshots

JPEG or 24-bit PNG (no alpha). Min length for any side: 320px. Max length for any side: 3840px.

Phone - 5 Screenshots

Between 3 and 10 PNGs or JPGs 800 x 480px, 1024 x 600px, 1280 x 720px, 1280 x 800px, 1920 x 1080px, 1920 x 1200px, or 2560 x 1600px (portrait or landscape)

Promo Graphics

1024 x 500 - Promotional Graphic