I want to make a picture where I have a lot of image elements that will repeat--e.g., stick figures in certain body positions. I'd like to be able to create a library of these image elements by drawing them or importing them as JPG/PNG/etc. and be able to select them and drag them from the library onto my main image. I want to resize them as needed. Then I want to be able to select them later and move them around. I also want to be able to combine elements to make a new element--for example, if I have a "hat" element and a "stick figure" element, then I want to be able to put the hat on the stick figure and add it to the library as a "stick figure wearing a hat" element.
What is this type of application called?