All the background images in SCI games are made up of pic resources. These are vectored images with a width of 320 and height of 190 pixels. Not only do they contain the background picture, but also the room's boundries and priorities.
Pic resources are stored in a vector format as opposed to a bitmap. This means that rather than storing the image's 320x190 pixels, it stores steps to draw the picture. For example, it may store something like "set color->blue", "draw line from (36,43) to (99,124)". This saved significant space, but is not as efficient speed-wise.
Each pic can store up to three seperate screens in it: Visual, Priority and Control.
Though SCI0 games are only 14 colors, pic resources contain 4 palettes. Each palette contains 40 colors. The colors in the palettes are each made up of two of the 16 colors. One palette is displayed at a time. The best use of this feature would be for showing the picture with both a day and a night look. This was used frequently in Quest for Glory.
You can use the picture editor To create and edit pics.