help posting pictures

[Jen_91909]

Help! So pics need to bee under 100k to be able to be uploaded. But a pic at 3x5 inches at 72dpi is still significantly bigger than that! Now, I see people uploading pics larger than 3x5 all the time and the quality certainly does not appear lower than 72dpi.

Can anybody solve the mystery for me?

If it helps, I''m on a mac and use photoshop.