[PHP] image problem

[nate]

I'm not sure if this is a problem with my php coding or html or the server or what, 
but I made a simple photo album that just basically lets users add a pic of themselves 
through a form and it records the url of their pic in a sql db and then i just display 
it on a page. Now the problem is only some pictures show up. Half are red x's and when 
i hit 'show picture' they still don't show up, yet when i click properties, copy the 
source of the image, and go to the source it shows up. Any idea what this is?
THANKS!