Image size for slideshow (not smugmug slideshow)

crockny

I'm creating a downloadable gallery for someone to pick and choose photos to create a slideshow to go with a piece of music. I'm not sure what size to pick - the drop down menu has Original and everything but Original and I'm not sure what that means ... the images need to look good on all platforms

leftquark

Original could expose your original high resolution images. “All but original” allows the largest possible size but while keeping your original safe. Any screen at any resolution will be able to be displayed. If you want to protect your photos from people accessing higher resolution copies than you can select a smaller size.

crockny

It's password protected for use by just one person so protection is not so much of an issue. But all but original sounds good ... as long as they display full size on a screen ...