In my game I have around 40 technologies for the player to research. For each technology I have a picture which goes along with it. The problem is the pictures are all of different subjects, have different lighting and colors and they don't really all 'go' together. Does anyone have any tips on how fix this? I tried doing some different filters in PS but that didn't really seem to help.

Post a few examples. Without knowing what they look like it will be difficult for anyone to give sound advice.

Did you simply find them in those 30,000+ stock pictures or online catalog? If so, you can't really get away from that. I have suffered the same problems and found that if I want the game to look consistent, I have to do my own art.

If you are not an artist, consider finding one on the net and have them contribute work to your project for either money or percentage of revenue or free.