Am I sinful for unintentionally burning pictures containing the name of Allah and the Kaaba, knowing the prohibition of drawing animate beings and having repented from that?

You bear no sin for what you have done, for burning is a legitimate means of disposing of anything that contains the mention of Allah. Indeed, Uthman ibn Affan (may Allah be pleased with him) ordered the burning of Mushafs that contained abrogated verses and recitations, and the Companions approved of his action.