Solved
Maximum Capacity of the Asset
What is the maximum capacity of the asset repository and the maximum size of a picture?
and is it feasible if two million people can click to open the image at the same time?
@johnnyliao, Assets repository size depends on the licensed AJO package. Probably your CSM can help get this information for you.
I don't think there's a limit to the maximum size of the picture but email size supports 100kb.
https://helpx.adobe.com/legal/product-descriptions/adobe-journey-optimizer.html
https://experienceleague.adobe.com/docs/journey-optimizer/using/email/create-email.html?lang=en
Thanks, Sathees