For those who design shower curtains, how big do you make your picture/graphics?

[Jadendreamer13]

I use a 6.8 x 6.8 inch art board created in Illustrator, then select all, copy to your clipboard, paste into Adobe Photoshop using the Design to Print extension (using the shower curtain template). Scale the graphic to fit the template and publish to Zazzle. The Adobe Design to Print extension scales the design to fit Zazzle’s template. No need to create an 81-inch piece of artwork when a small piece of art with scaled down dimensions works just fine. If you don’t have Illustrator and Photoshop, you can get subscriptions for $22.00/month for each.

[PenguinPower]

That only works because Illustrator graphics are vectors... for non-vector artwork formats, you do need to create very large file. I don't remember exactly what it is off of the top of my head, but I'm pretty sure that it's something just a little less than 6,000 pixels square needed for a shower curtain. (5832 would be 81" at 72 ppi)

[Jadendreamer13]

It still works with high-quality png files. The key is using Adobe Design to Print as the Photoshop interface. 

[PenguinPower]

It may fool the warning… but a small png file (or any other raster format) will not look ok if enlarged to the size of a shower curtain…