i have the same issue as @Anonymous .
when i run the report with the option rc:Toolbar=true, the images would be displayed.
One of the identified problems is that the image url is an http url, although the report has an https url.
The images are embeded images, so i don't have a idea how to publish them as a https.
One more thing i found is, the ssrs-report will be rendered in a different mode if we use the rc:Toolbar=false or true.
In the ssrs ReportServer.dbo.ExecutionLog can be seen, that if we use rc:Toolbar=false the report-format will be a HTML5, if we use rc:Toolbar=true, the report-format will be a RPL.
Actually we use the version 15.0.1102.911 of the ssrs-service.
On the release-notes for SQL Server Reporting Services (SSRS) 2017 and later this issue would be mentioned on the version 14.0.600.1109, 2019/02/12, but the version 15 would not be explicit mentioned.