image on lwip http server

I ve been messing around with the http server example (netconn) of the lwip stack in stm32f4 dev board. the example works well and I see the example web page without probles. The problem apears when I change the web files with my owns, in this case the pictures don't show up. I have used the makefsdata with multiple options and variations, I have also used multiple pictures and file formats (pnj, jpg, gif...) but the result is the same. any idea of how to make this work it's apreciated.