Piχtor.io
https://pixtor.io
To use Piχtorio, you upload an image, and choose which tiles you want to draw with. A scaling factor lets you tune the size of the resulting blueprint, and you can also choose and re-order the tiles to tune the aesthetics.
The app applies the κ-Means clustering algorithm to your image to reduce its colors to the number of tiles you have selected. You may need to tinker a little bit to get a good result. Images with little color variation get cleaner results if you select fewer tiles. Some pictures will work better than others. The preview is very rough; it is better to look at the result in-game.
You can put your dog into your base too!

Or your god!

Or Pikachu!

Or the moon!

The code is open-source. I have tested it a bit, but I expect there are still bugs. Also the server is kind of weak, and κ-Means is kind of expensive, so please be patient. Don't hesitate to contact me directly or via GitHub if you have errors; I want to fix them! Contributions are welcomed and encouraged.
I hope you enjoy this tool! Please send me screenshots of your creations! They will make my day.
- mlgarrett