If you start a program using this function and want to leave it running in the background, you have to make sure that the output of that program is redirected to a file or some other output stream or else PHP will hang until the execution of the program ends.
En fixant le résultat du contenu (Content-Type) à "image / gif "puis en appelant pbmplus pour obtenir une image gif, vous pouvez créer des scripts PHP qui retourne des images.