Got it! Yes, sometimes using cloud resources like DropBox and Google Drive, these will work as links, but can be problematic using them as HTML image resources. I think I've been able to get DropBox images to work. I can check into Google Drive.
From the additional information you've provided, I think a good way to go is for you to enter a "Chart URL" into the song field.
The resource is then available through the 'i' action on the song detail set list section, or the song list actions. Your members can click the "Chart URL" link:
Which will display the chart. This example uses a Google Drive resource:
Do you think that will get you what you need?
--Ethan