Using these 'found' pictures could cause problems, as you may be infringing copyright (if you copying them) and trade mark mark law if any of the images have been registered as trade marks.
Assuming that you only use an original image cut out from a comic etc, then that would not infringe copyright as there would be no copying involved, although there might be a claim arising from a more obscure part of copyright law, namely, treating an image in a derogatory way. However I don't think such a claim has any merit and would be unlikely to succeed.
The trade mark issue is more likely to be the one which Trading Standards will wish to discuss. It would be worth checking with the IPO website
to see if any of the characters you have used are registered as graphical marks (and not just their names) - here's an example for Hello Kitty
. If you find any entries, check which classes they are registered in. The one most relevant to you is Class 14: Jewellery and possibly Class 28: Playthings.
However even if you do not find any other graphical marks which match your characters, there may well be grounds for a claim of passing-off. This means that by using the characters within your jewellery you are misrepresenting the items as either originating from or are authorised by the owners of the original characters, so trading on their goodwill. To guard against this, you would need very prominent disclaimers to show that you goods are unofficial and unconnected with Disney, Hello Kitty, etc. The problem is that the courts look at what is in the mind of the customer rather than at your intentions or motives. If there is any doubt in a customer's mind, then that will be hard for you to provide a sufficient defence, given that the other two elements of a passing-off action - namely existing goodwill in the originals, and damage through loss of sales or dilution of reputation - are pretty easy to establish. If you have a website or are trading through ebay etc, make sure you put your disclaimer in a very prominent position, and don't use the name of the character in any description, for instance 'a Hello Kitty bracelet', because this will immediately put the brand into the mind of the customer, and this can be used against you when it comes to establishing misrepresentation. If you think this anonymising will make it hard to sell these items, then you will see exactly why passing-off may apply here, because you would be seeking to ride on the popularity of someone else's intellectual property.