Below is a resource list of all the different standard image sizes across the Simplero admin settings.
Site card image 700 x 380 pixels
Logos on a site - At least 32 pixels tall
Course catalog image 700 × 380 pixels
Course and Lessons thumbnails to be compatible with Simplero App view: aspect ratio 16/9 with a minimum width of 800px. For example, 800x450 px.
Found in legacy builder
Product catalog image 800x450 pixels (16:9 ratio)
Email header image 600 pixels wide
Account logo 1000 x 200 pixels
Account icon 150 x 150 pixels
Email logo: max. 200 x 200 pixels
Account header image (accounts with spaces only) 980 pixels wide and less than 400 pixels tall.
Attachment images 1200 x 800 are recommended but any 3:2 aspect ratio will work