How to use your own logo on ships

There are two possibilities here. If you bought your game via Steam, your logo folder can be found at /Documents/Egosoft/X4/[Numbers]/logos/.
If you did not buy the game via Steam, the logo folder will be at /Documents/Egosoft/X4/logos/.
If you are unsure as to where to put the folder, put it in the same one with your save folder.

Example: /Documents/Egosoft/X4/[Numbers]/logos/

For the [Numbers] folder to be generated you will need at least one save-game, so the first step is to save your game at least once. After that, create the logos directory inside of the [Numbers] folder. If you did not buy the game via Steam, the [Numbers] folder might not be created. If that is the case, create the logos folder in the same directory where your save folder is.

Valid file formats are .BMP, .DDS, .GIF, .JPG, .PNG and .TGA.
Transparency in images should work as expected, but animations in GIFs will not play.

The images you place inside the logos folder must be square and a power of two. A valid size would be 128x128, 256x256, 512x512, ... and so on. The standard size used by the default logos is 256x256.

This step is optional, but it will make your logo look better. If you are not interested, scroll to the next section.

Glow maps and normal maps are supported. They are placed in the logos folder alongside your logo. You need to follow a naming convention for this to work.

Logo: logoname_[number].png
Glow: logoname_[number]_glow.png
Normal: logoname_[number]_normal.png

The [number] part must be the same for all three. It's a two digit number, so make sure you write 01, 02 and 03 instead of 1, 2 and 3.

To generate a quick normal map, you can use this link: http://cpetry.github.io/NormalMap-Online/
Upload your logo by clicking on the left of the three pictures to get a preview of how it will look. Make sure you select the Plane model in the options.

Example logo without maps:
https://steamuserimages-a.akamaihd.net/ugc/955223229304444022/DA13E8FD2BF40D16064BED095885AE071A6F5AEA/

Functional normal map:
https://steamuserimages-a.akamaihd.net/ugc/964230781512902024/840F23EC30591F4EF0ED408654FEA9A172F083B2/
(Thank you, Jinarra)

After you place the logo inside the folder, you might have to restart the game. The logo will then show up for selection in the game. Press ENTER, click the tab Player Information, go to your Empire Overview and then scroll down to Custom Logos.

Hope that helped. If there are things I missed in my explanation please let me know.

https://www.youtube.com/watch?v=F7pUGET1VbA (Thank you, Kane Hart)