Printed images will almost always look slightly different when printed as compared to when they are viewed on a digital monitor simply due to the difference in light properties (direct vs reflected).  When a monitor's brightness is set too high, images will appear brighter on the screen than the resulting prints.
To achieve the closest color and brightness match between your digital photography/art and your printed images; we recommend using a high quality monitor along with a calibration tool from a company such as X-Rite or Datacolor to fine-tune your digital display. Save your final edited print files in the JPEG file format with an embedded sRGB color space before uploading to our online portal.