First off, big thanks to the team for allowing this feature! And for putting up with my constant request @anoek @GreenAsJade 
This guide is to walk users through using images unlocked on Tsumego Dragon on OGS. These links can come from any source however.
To get started, all you have to do is hover your mouse over your username in the top right corner.
A dropdown window will appear.
At the bottom of this dropdown there is a toggle for customizing stones. Turn it on.
This is the section the place you can customize the goban to your liking.
In this first section is the goban. The input field is for an img url. This does support png transparent backgrounds. The second box, the left brown color, is the color of the goban. If your image completely covers the goban then you don’t need to touch this. The black color box is the line color. For either color you can click to open up the color picker window.
The second row is the second move, or the white stone. The color box will change the stones color. The input will also take in an img url.
Finally, the same with the first move, or black stone.
Now on to Tsumego Dragon. Once you are logged in you will need to go to your profile.
You can find the link to the profile at the top of the page.
On the left side of the page you will see a sub menu.
Click the OGS tab.
This will open the OGS settings. From here you can copy all of the images for your convivence.
The first two will copy the hex codes of the color. Simple click the copy icon.
Back on OGS you can click the color boxes to input the hex codes. Some browsers have a bug where the color picker will not allow pasting. If this is the case just paste the hex code somewhere else and manually type it in.
At the bottom of the color picker you will find a dropdown. Click this until it shows the hex code. Then input the hex code from Tsumego Dragon.
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For the stones it is even easier. Click the copy icon for each stone and then navigate back to OGS.
And paste them into the input fields.
The last step is to simply click the custom field buttons. (The squares) Do this for the board and both stones.
Now your Goban will have the new graphics.
For a bonus, you can set your profile picture to your current dragon selection. Just click the download icon to download your profile image.
Back on OGS, hover the top right again.
Click profile
On your profile, under your profile image, click the Edit button.
Click the image to upload the image you downloaded from Tsumego Dragon
Once done click the save button.
Enjoy!
Clossius
P.S. I would love to see people’s Goban! Regardless of source~
