I would seriously reconsider using generic or stock pictures, or even animated cartoons.   

The last thing you want is for people to be mass producing these and when the copyright owners ask you to cease and desist producing these with their images, you will have no control of others doing it. 

They will not make a claim straight away, but will do so when they can get the most out of you.   

Check out what happened to the Takeicoin and George Takei. 
Just using his image was a big show stopper for them they had to re-brand and also change the name completely, don't attract unwanted attention. 

When are looking to have these ready? I can help you with finding images.