data-structure.js

var layers = [
  { 
    image: 'image 1', 
    x1: 0, 
    y1: 0, 
    x2: 100, 
    y2: 100  
  },
  { 
    image: 'image 2', 
    x1: 10, 
    y1: 10, 
    x2: 20, 
    y2: 20  
  },
  { 
    text: 'cool stuff', 
    x1: 10, 
    y1: 10, 
    x2: 20, 
    y2: 20  
  }
]

Object model:

{ 
  text: String, 
  image: String,
  x1: Number,
  y1: Number,
  x2: Number,
  y2: Number
}

References:

• http://aheckmann.github.io/gm/docs.html#drawText
• https://github.com/aheckmann/gm#composite