Because this game doesn't support Steam Overlay (the shift+tab thing). Without it, Steam can't take screenshots. There's also a common method around the internet that requires you creating some folders and copying your screenshots there, renaming them and stuff like that. That is required to upload custom screenshots, but the method being taught doesn't work, unfortunately.

• You'll need a program to take screenshots with. You can just print your screen, alt+tab and paste it into paint, but I don't recommend doing that. There are easier ways to do it. I recommend Bandicam. But you can also use Fraps, Gerforce Experience or any program of your choice.
  
  
• You'll also need SteaScree. This is the most important thing. SteaScree is a free open source program designed solely for uploading screenshots for Steam games that don't support overlay. You can download it directly from their site[steascree.download].

SteaScree is very intuitive and easy to use. Just by opening their website (linked in the previous section of this guide), you'll have every info you may need right in front of you. You just have to put the images into it and the program does everything by itself. Here's a very nice image tutorial taken directly from SteaScree's site:

SteaScree will automatically convert any screenshot you have to the required .jpeg, adjust their file size, create required folders and rename the files to Steam's required standard. Just open the program and it will tell you all you need to do. You only need to have the screenshots beforehand (see - previous section of this guide).

After you're done with SteaScree, open Steam again (the program will ask you to close it at one point) and click on Tomb Raider: Underworld. Then, scroll down. Like in the picture below.


You will see your screenshots and this button. Click on it.

Then, just select your screenshots and upload them!

To SteaScree and it's creator, Foyl. This tool is absolutely amazing.

Please rate!