How would you mix pictures together? Example = Sora and Link fighting.
Or, use a slide show program to put both pitcures next to, or on each other. Control + Click on both, then go to the top menu and find "Group". You can now move both pictures as one. If you want to save the picture, right click on it, and find "Save Picture".
Just a guess....
Adobe Photoshop and a little schooling.