Everything that has been recorded or written down since the mid-80s in tangible form has a copyright attached to it, so those pictures belong to someone. The songs also belong to the people that wrote it. Copyright provides absolute control to the copy holder the right to control distribution, reproduction, and performance of their work. That control is then constrained a bit by what is called "fair use" doctrine, but what you're doing isn't going to be part of that.
So, to the letter of the law, yes, you have committed a tort (as opposed to a crime) and could be liable to the copyright owner. In a practical sense, I doubt you have much to worry about. If you get a cease and deist letter then simply apologize and then cease and desist. Damages have to be shown in order to win a monetary award, so unless you are raking in the big bucks and the copyright holder can demonstrate actual damages (I lost X amount of business as a result of these YouTube videos) then I'd guess the most that will come out of a courtroom is an injunction against you to prohibit the use of the work.
YouTube (and any service dealing with user generated content) are particular about copyright infringement. If they don't take active steps to prevent it, then they are contributors to it and are also liable for your tort. And they have deep pockets that draw lawsuits like flies to old meat. I'd bet that if there is a problem with what you're doing, you'll hear from YouTube about it long before you hear from the copyright owner.
Someday we'll win this thing...