From the picture on the left, to the picture on the right, I'm going to explain every edit in sequence not only as a learning tool for someone else, but to help me in the future as well. I'm no artist, just a guy who has GIMP and can copy/paste.
1) The first thing I wanted to do was make the last vehicle slot appear to be in use. This was done by copying the "selected region" to the extra space at the end there. Afterwords I copied a new Muscle image 1 image over the original to hide the old selector. I made sure to keep the icons over the selector as well. The faded part of the selector was achieved by using a blend tool to create the blended region. Looking at it now, the colors don't match 100% but the effect was still there after all was said and done.
2) So I got the vehicle selected, now I had to merge the vehicle in. I first started with a photo of the truck on trackside that was kinda at the right angle. I took a large eraser to it, cutting off a lot of the picture, then went in with a smaller eraser to cut as close to the truck as possible without cutting into it. Finally I went in with a 2-pixel eraser for the finalized product, making sure that the windows were erased properly too. I did that all by mouse. Then I resized the image to fit the scene, making sure it at least looked like it could fit there while also covering up the Muscle 1, which turned out to be really easy as the colors of the car stand out. The hard part was the shadows.
3) After the top of the car was covered using background pieces, the bottom of the car kinda stuck out, as well as the shadows didn't match up with the truck. I was able to fix both of these issues by copy/pasting parts of the floor to match the shape of the truck. The corner shadow was cut using a free select tool, and the shadows under the front of the truck were copied from the front of the truck. It was somewhere between Step 2 and 3 that I decided to colorify the whole truck in purple because the last time I saw a car without textures it was a solid purple color. Now I had a back story. In the middle of the process as well, I created a new layer for the menu so that it overlapped the truck.
4) Once the photo was done, I came up with a convincing story. I knew that by creating this hoax my credibility would drop even after coming out that it was fake. I intended it to be a joke, and it is probably shrugged off as such.
Flaws: The first issue I ran into was on the driver side door window. It had a matching brace to the passenger side window, but for some reason I couldn't retain it's shape when I was erasing around it, so I just removed it. After I had posted the photo, a couple more things stood out to me as flaws. Firstly I noticed under the front of the truck was an obvious texture repeat. To fix that I would paste more textures over it to make it look like less of a pattern. The other thing is that under the side of the truck, the shadow doesn't match up with the front of the truck. There is also a repeated texture, but this one looked naturally like a repeated texture. The only thing someone else mentioned was that the tire appears shaved off. This is true to the fact that the truck is semi-clipped in the ground in the original photo. If someone had mentioned that from the forums, I would have explained to them that the truck was clipping in the garage, which appears realistic.
Conclusion: I had also intended to paint the truck texture to change the lighting of it, however after I turned it purple, it looked like it fit in the garage, so I left it. The edits took an appropriate amount of time over 2 days. By that I mean minutes turned to hours, and I never kept track of the time. What I learned from this is that the final product could have had more work, just a little. Also, not once did I use the paintbrush. This was all achieved with copy/paste and lots of fine erasing.