This depends on where. Basically the resolution should be as good as possible and the size as small as possible. The larger the image, the longer the loading process. Many formats and sizes are possible from the tool. Here you get an overview of recommendations:  


  • Header image: 
    • Size: max. 2 MB
    • Format: min. width: 1200 pixels, height: freely definable
  • Photo banners: 
    • Size: less than 1 MB
    • Format: 3696 x 2456 Pixel (png)
  • Pictures in email:
    • Size: Automatically optimized by the tool during upload
    • Format: Various possible
  • Picture on the web page (in continuous text):
    • Size: Automatically optimized by the tool during upload
    • Format: Various possible
  • Photo gallery: 
    • Size: 2-8 MB (Max. 25 MB)
    • Format: 4176 × 2784 pixels or equal dimensions larger/smaller