All below screenshots taken with my showrooms and Content Manager.
This mod was created by me and contains 9 showrooms and 14 presets for Content Manager Custom previews.
Download the mod from this page, extract it and copy the showrooms to "\Assetto Corsa\content\showroom\" and the presets to "C:\Users\<YOUR_USERNAME>\AppData\Local\AcTools Content Manager\Presets\Custom Previews\".
You can use my showroom with the original Kunos showroom but I recommend using Content Manager. If you don't have it download the program from here http://www.assettocorsa.net/forum/index.php?threads/content-manager-aka-alternative-launcher.33824/ or from here http://acstuff.ru/app/
Once in Content Manager, select a car, open one of my presets and take a screenshot. That's it!
Open Content Manager, go to content and select a car. Then click Update previews>>Options.
Then click "Switch To CM Showroom" if you have not done yet.
Then go to scene and select a preset or a showroom and take a screenshot by clicking the [+] icon.
Remember to have the latest version of Content Manager, version 0.8.882.17282 or higher, by enabling "Update to non-tested versions" option in Settings>Content manager>General.