To can diced tomatoes you first need to peel the tomatoes. To peel tomatoes you first core them. I have a handy little gadget that takes the core out.
Then dip the tomatoes in boiling water for 30-60 seconds. I normally go 60 seconds. The skins will begin to split. Take out of the water and put in ice water to cool.
Once cool just pull the peel right off. The easily slip off. Once in a while you have a spot or two that get stubborn and I use a knife to help get it off.
After the tomatoes are peeled just dice them up and put them into your jars. You do need to add some acid to your jars. I normally use lemon juice but I was out. So I used citric acid. If you use lemon juice you need to add 1 tablespoon of bottled lemon juice to pints and 2 tablespoons to quarts. If you use citric acid you need to use 1/4 teaspoon for pints and 1/2 teaspoon for quarts. fill with tomatoes pushing down to fill jar. Leave a 1/2 inch head space. Wipe rims clean and adjust caps. Process in a boiling water bath for 35 minutes for pints and 45 minutes for quarts.