You’ll notice when uploading .zip file order scans, the size limitation warning as shown in the screenshot below. It states the maximum file-size of a single order scan should be no more than 1500 KB (or 1.5MB). And the maximum resolution should not exceed 1000 pixels x 1200 pixels.
What should you do if your file size is too big?
There are many different programs (that help manipulate images in bulk) on the internet that allow you to reduce that size (both in size and resolution) of your large images.
We at Showroom Exchange use ACDSee (standard version): http://www.acdsee.com/en/products/acdsee-18
ACDSee allows us to bulk reduce multiple images before uploading.
There are free options. here is 1 link.
NOTE: This is not an endorsement: