In Leaflet, a marker is made from two images: an image that represents the marker and a second image that serves as the shadow to create depth. When you download Leaflet, there is an images folder. This folder contains the default marker: the blue pin that you have seen in your maps and a small shadow image. The images are named marker-icon.png and marker-shadow.png. The default marker and shadow are shown in the following screenshots:
To create your own custom marker, you will need to draw an image in a painting application. In this example, you will use the free GNU Image Manipulation Program (GIMP). GIMP is a powerful imaging program that is similar to Adobe Photoshop which runs on most operating systems and is completely free. To download GIMP, go to http://www.gimp.org/downloads/ and click on Download GIMP 2.8.10.