I have been doing a lot of thumbnail creation for old workshop mods and broadcast overlays so I thought I'd write a tutorial to show you how I do it. Note: This process won't replace thumbnails of mods with cars under grey sheets, for that you need to make an update to a mod (something I may make a tutorial on how to do later).
We will be using the inbuilt "sideview_ui" showroom for this but there are some custom showrooms that do the same job:
SHOWROOM ICON CARSET FOR RFACTOR 2 UI by Lucas Clezar
FIrstly we need to setup rFactor 2 so it captures the correct format of images. Make sure your rFactor 2 game is closed before proceeding.
Navigate to your "rFactor 2\UserData\player" folder and find the file "player.json". You can open this file with a text editor like Notepad or my personal favourite Notepad++.
Search within the text for the word "screenshot". It should lead you to a line for "Screenshot Format". Explained in the comment underneath will show you what you can set this value too. We want the format of our thumbnails to be "png" which is a format that contains transparency so we set it to "3". Save and close this file.
Now we can open rFactor 2 and head to the Settings - Assign Controls. Click on the "Assists and Gameplay" section and look for the entry for "screenshot". By default this is probably set to F12 which is normally conflicting with the Steam screenshot button and may produce duplicate screenshots. For this reason I have set it to F11.
While we are in the Settings menu select the Graphics section. If you look at the bottom of the 2nd column you will see an option to select a showroom. Clicking the left and right chevrons will select between the showrooms you have installed. Set to the "sideview_ui" and head back to the main menu.
For this capturing example I will be using the Formula Renault 3.5 mod on workshop (there is a reason why but we'll get to that).
Go to Singleplayer and "select car". Find the car you want to capture and over on the right press the "customise" button. Now a preview of the car will open... but something is wrong!
For some older mods this does happen with the showroom we chose, so we will have to use a different showroom I listed in the introduction.
This is the capture we get from the "icone_side" showroom which is MUCH better!
In some showrooms you have the ability to zoom in and out with the right mouse button to get your screenshot to be as large as possible. This can sometimes be buggy leaving the car too zoomed in to capture so we have to back out and try again.
We want to just capture the car so firstly we need to get rid of the background. If we press the two squares icon to the right of the plus symbol the background will go black. This means that it is now transparent!
Also to help us, let's get rid of the top menu by pressing the padlock on the top right.
Now press your screenshot button you set earlier.... and VOILA!
Move your mouse up to the top of the screen to get your menu back and exit the showroom.
Depending on what you are doing with this capture it might need some adjustment.
Your screenshot will have been saved in your "rFactor 2\UserData\ScreenShots" folder.
Open your graphics app of choice (in my case it's Photoshop). There is free online editor you can also use called Pixlr.
Open the image you just captured. Magic wand select the background, invert selection and then crop. You are then left with a thumbnail without the large background.
I have created a Photoshop action to make this process a bit quicker and if I have a batch of screenshots I can apply it to all of them.
There ya go! You now have the ability to make thumbnails of cars in rFactor 2 to use however you want!