Are the marks on the skin starting out like a blister or pox mark?
Also it has slight swellings at both the "wrists"...this could be caused by a few things including infection or gout.
I really think you need to take it to a vet.
Sounds like your chameleon may not be getting any proper UVB and you need to provide supplements and gutload/feed the insects properly.
Since most of the feeder insects have a poor ratio of calcium to phos., its important to dust the insects before feeding them to the chameleon at most feedings with a phosphorus-free calcium powder (like rep-cal).
I also dust twice a month with a phos.-free calcium/D3 powder to ensure that the chameleon gets some D3 without overdoing it. D3 from supplements can build up in the system and cause problems. D3 produced from exposure to UVB shouldn't as long as the chameleon can move in and out of it.
I also dust with a vitamin powder that has a beta carotene source of vitamin A. Beta carotene (prOformed) vitamin A sources will not build up in the system like prEformed sources will but there is controversy as to whether all/any chameleons can convert it so some people give a little prEformed once in a while. Excess prEformed vitamin A may prevent the D3 from doing its job and push the chameleon towards MBD so be careful if you do use it.
Without these supplements you are lucky that your chameleon hasn't already shown signs of MBD. Calcium, phos., D3 and vitamin A are all important nutrients for bone health and other systems in the chameleon and they need to be in balance. You need to look at what you supplement with, what you feed the insects and what you feed to the chameleon when trying to balance them.
Crickets, locusts, roaches, superworms can be gutloaded with a variety of greens (dandelions, kale, collards, endive, escarole, etc.) and veggies (carrots, squash, zucchini, sweet potato, sweet red pepper, etc.)
The veiled can be offered the same greens and veggies and a SMALL amount of fruit (apple, pear, melon, berries, etc.).
Its important not to leave water laying stagnant in the bottom of the cage or in a dish in the cage. It could very well be part of your chameleon's problem.