Triangula
Generate high-quality triangulated and polygonal art from images
...It works best with images smaller than 3000px and with fewer than 3000 points, typically producing an optimal result within a couple of minutes. For a full explanation of the algorithm, see this page in the wiki. You can try the algorithm out in your browser, but the desktop app will typically be 20-50x faster. If the app isn't running on Linux, go to the Permissions tab in the executable's properties and tick `Allow executing file as program`. For almost all cases, only changing the number of points and leaving all other options with their default values will generate an optimal result. ...