AstroImageJ (AIJ) has become the industry standard for measuring the Flux variations for Exoplanet transits. Additionally, there is a component of this program that permits accurate measurements of Double Stars. The software will also provide a differential magnitude between the Double Stars as well as relate the CCD image to surrounding known stars from the SIMBAD catalog. As with all astrometric measurements, you will need to know where the image is located in the sky. Therefore, each image will have to be calibrated with World Coordinate System (WCS) embedded. Then, each measurement can occur accurately in AIJ. This lesson presumes you have viewed the following lesson videos, or at least have an understanding of: Astrometry Overview, Magnitudes, and WCS Coordinates.
STRONG SUGGESTION: Watch this video in its entirety first before starting a measurement. Then, come back and follow along with the steps. It is important that you achieve an overview of how this works in AIJ before beginning.