"""
Image tooltip
-------------
This example shows how to render images in tooltips.
Either URLs or local file paths can be used to reference
the images.
"""
# category: interactive charts

import altair as alt
import pandas as pd

source = pd.DataFrame.from_records(
    [{'a': 1, 'b': 1, 'image': 'https://altair-viz.github.io/_static/altair-logo-light.png'},
     {'a': 2, 'b': 2, 'image': 'https://avatars.githubusercontent.com/u/11796929?s=200&v=4'}]
)
alt.Chart(source).mark_circle(size=200).encode(
    x='a',
    y='b',
    tooltip=['image']  # Must be a list for the image to render
)

@@ -146,16 +146,142 @@
  images.
+ To render the image, you must use the special%0Acolumn name %22image%22 in your data and pass it as a list to%0Athe tooltip encoding.
 %0A%22%22%22%0A# c
@@ -691,30 +691,40 @@
 ist 
-for the image to render
+containing a field called %22image%22
 %0A)%0A

Clarify that a special field name is required to render images in tooltips (#2570)