I have the same problem. I use an Epson printer, I print from Photoshop and that might be the problem because when I print from the default Windows picture viewer the colours and brightness is much better... what gives!?
Well I managed to perfectly compensate for the darkness by adjusting the mid levels on the image and then printing them out again.
-Print out a test image (I would suggest printing one of the photos of the characters....Like the pic with Nate and Sully)
-After the image is printed out, open two copies that same image in Photoshop and then open the "levels" feature on one of the two copies. Take the middle level slider and adjust it until the image on the screen is as close as possible to the same darkness as the printed image. and then commit to the changes.
- After that image has been darkened, once again open the "levels" feature on that same image and then use the middle levels slider to get the image back to the correct brightness.
Use the untouched copy of the image as reference.
-Once you get the image back to the correct brightness, write down the number that was indicated on the slider tool when you moved the middle slider. On my image I had to slide the middle slider up to 2.30...It may be different on your computer.
-Once you figured out the level number, go to the untouched copy of the image, open the levels feature and move the middle slider until it reaches that level number.
THe image will probably look extremely bright, but once it goes to print it should darken up to look right.
Let me know if that works.
Keep that number handy for future prints.
DS