1. A method for a portable computing device having an image sensor and a screen on a same side of the portable computing device to read a reaction area on a test strip, which is located in a peripheral device, the method comprising: providing light with a portion of the screen to the peripheral device, which is placed over the image sensor and the portion of the screen and directs the light from the portion of the screen to illuminate the reaction area in a manner that the image sensor on the same side is impinged by the light passing through the reaction area or by the light scattered or reflected from the reaction area; capturing an image with the image sensor substantially free from ambient light, wherein the image includes the reaction area; and determining an analyte characteristic based on a color of the captured reaction area in the image.