Based on the pictures and the cats I've had in the past, I think you should be feeding about three-quarters of a normal sized can of cat food per day, and NO dry food or treats.
My mother had an obese dog. She shortened its life by feeling that it was cruel not to feed her when she asked for food. My mother couldn't understand that she was actually doing the dog a disservice by feeding it by demand.
Ignore your cat's pleas for food, and he'll soon get used to the idea and settle down to the new regime. I agree with what others have said regarding exercise. Lots of play with fishing rod toys or a laser toy.
Your cat does look overweight, it shows especially on the tummy and shoulder area. Cats live longer if they are lean. They're only too thin if you can feel the vertebrae when stroking down the back. Thin cats play more and are generally healthier.
Cat Body Condition Chart
Thin Cat
* Ribs, lumbar vertebrae and pelvic bones easily visible
* Thin neck and narrow waist
* Obvious abdominal tuck
* No fat in flank folds, folds often absent
Underweight Cat
* Backbone and ribs easily palpable
* Minimal fat covering
* Minimal waist when viewed from above
* Slightly tucked abdomen
Ideal Cat
* Ribs palpable, but not visible
* Slight waist observed behind ribs when viewed from above
* Abdomen tucked up, flank fold present
Overweight Cat
* Slight increase in fat over ribs, but still easily palpable
* Abdomen slightly rounded, flanks concave
* Flank folds hang down with moderate amount of fat-jiggle noted when walking
Obese Cat
* Ribs and backbone not easily palpable under a heavy fat covering
* Abdomen rounded; waist barely visible to absent
* Prominent flank folds which sway from side to side when walking
There are pics relating to this at this link:
http://www.kittens-lair.net/cat-health/the-ideal-weight-for-a-cat.html