Add a gallery example for the fig.image() method (#777)

Co-authored-by: Dongdong Tian <[email protected]>

Author: michaelgrund

examples/gallery/plot/image.py

@@ -0,0 +1,29 @@
+"""
+Images or EPS files on maps
+---------------------------
+The :meth:`pygmt.Figure.image` method can be used to read and 
+place a raster image file or an Encapsulated PostScript file
+on a map. We must specify the file as *str* via the ``imagefile`` 
+argument or simply use the filename as first argument. You can 
+also use a full URL pointing to your desired image. The ``position`` 
+argument allows us to set a reference point on the map for the image.
+
+For more advanced style options, see the full option list 
+at :gmt-docs:`image.html`.
+"""
+
+import pygmt
+
+fig = pygmt.Figure()
+
+fig.basemap(region=[0, 2, 0, 2], projection="X6c", frame=True)
+
+# place and center the GMT logo from the GMT website to the position 1/1
+# on a basemap and draw a rectangular border around the image
+fig.image(
+    imagefile="https://www.generic-mapping-tools.org/_static/gmt-logo.png",
+    position="g1/1+w3c+jCM",
+    box=True,
+)
+
+fig.show()