Converting a sequences of images to a video with ffmpeg

Question

I'm trying ffmpeg to convert sequence of images to a single video, but nothing happened and no any error message is shown. Below is the shell command I've used (invoked via PHP's shell_exec):

ffmpeg -i events/dream_theatre.jpg events/output.avi &

I just want to test first with single image and trying this in shared hosting server. No error message or any message is shown with this. I've a root access to server machine.