I saw this image in an answer on another question
Where is it from? I am not a highly vested Star Wars fan but I am a person who is very interested in the back stories and physical abilities or devices used with certain characters and stories.
That image is from Star Wars Blueprints: The Ultimate Collection, published by DK Books.
The full panel is show below.
If you're interested in Darth specifically, you might also want to consider getting hold of the Darth Vader: A 3-D Reconstruction Log factbook. It shows Vader in great detail and covers every part of his bodysuit.
This appears to be from Star Wars Blueprints: The Ultimate Collection.
While I don't have a copy to 100% confirm this against the contents of the book, the cover art matches the image.