How can i cut the first 11 characters from a string?

How can I cut the first 11 characters from a string, I would like to display some name of some images, but all my images has 11 random characters and a _ before the actual name of the picture shows, I would like to get rid of these 11 characters before displaying the name.

I tried this:

substr($foto_filename,0,11)

But it does the opposite.