I've taken the liberty of downloading your image and adding a box to indicate the position of the comet at 2300 UT Sep 3rd. Sorry but I don't see any sign of the comet within it.
(Broken link as I seem to be having problems uploading to my web hosting service. Sometimes happens ... I'll try uploading again when it's fixed)
If it helps at all with processing.... I find the best thing to do is to make an S shaped curve which rises very steeply just above the level of the background fog, this brings faint low contrast objects into as much relief as you can get. For comets it also helps a lot to turn the colour saturation right up as the cometary coma glows a distinctive green colour in digital shots.
