Please note that, once printed, a photo will always be a little darker than when you see it on a back-lit screen.
Images may appear lighter on screen as most modern monitors have a backlight; a backlight is a form of illumination used in liquid crystal displays (LCDs). As LCDs do not produce light themselves, they need illumination to produce a visible image.
Backlights illuminate the LCD from the side or back of the display panel.
This is why your images may appear darker when they are printed.
As a consequence, if your image appears dark on the screen, we advise you to lighten it or not to use it.
Why color looks different on a screen versus printed
Your computer monitor is made up light-emitting diodes as pixels. Those pixels mix the colors Red, Green, and Blue (RGB) to make all the colors on your screen.
Ink on paper, however, is obviously not made up of lights and pixels. In print we mix Cyan, Magenta, Yellow, and Black ink, to make most colors (CMYK). This is also true of your inkjet printer at home.
Because we are moving from one medium (lights on a computer screen) to another (ink on paper), the representation on your screen is not always accurate to what will print. This is especially true of blues and oranges.