Unfortunately the ppi myth won't die. You hear 72 and 96 for screen resolutions that were common in low resolution 1990s monitors.
Only pixels count and you just need to be sure they match your target, the projector screen. I would say experiment until you find the dimensions you that look sharp on the screen
300 ppi is a standard and basically for an offset press. It is a print, not screen specification. Inches refer to paper not screen.
800 pixels divided by 300 ppi = 2.66 inches if they want to print it at that setting on paper.
Add to the confusion caused when shops use dpi (device units) and ppi (screen units) interchangeably.
I was wondering about this sort of thing the other day: can you make a Photoshop document that has NO resolution - just pixel dimension, no physical units. I tried, but Photoshop wouldn't let me create such a doc.
So, if the resolution has to be something, might as well humor these competition people, and make it 300.
Semaphoric, actually Photoshop will.
Save for web takes out the ppi spec in the Metadata. Thus Photoshop will fill in 72, but Windows properties will fill in 96.
I use Exiftool by Phil Harvey and the ppi field is not there. So some programs "fills in the blank."
I found this out when a user was confused why Photoshop Mac version reported 72 ppi but Windows files properties reported 96 ppi, based on the old 640 x 480 Windows standard. He was in a contest and the spec was given as 72 ppi and he didn't know what was going on. Saving directly to jpeg and png will include that spec in the metadata to avoid "the changing ppi."
I agree. Humor them especially if they get bureaucratic about the rules they set.
Thanks for putting this issue to rest. The link in your email is just what I have always wanted.