Currently working through Integrating Visualforce and Google Charts.
After a bit of debugging, I managed to get my code to create a working URL for a chart, e.g.:
However, the with this chart does not render as expected.
I tried replacing "{!chartUrl}" with "https://sledgehammer.eu3.visual.force.com/img/seasonLogos/2015_winter_aloha.png" (the SFDC logo) and confirmed that the logo will appear when the chart is expected to appear.
So, I'm guessing the problem has to do with cross-site security?
Is there a fix for this?