The most likely reason for the error that you are seeing is that there's a problem with the web services configuration. The most likely problem is that the image is greater than 16Kb, so Axis needs to save the attachment to a temporary directory. A useful test is to make sure that images smaller than 16Kb work with no problems.
Your quickest workaround is to upload the picture via the JasperServer web UI. Then your report should work as expected. If so, it's also validation that the problem is with web services (not with the repository database or some other component).
The most likely permanent solution is to recursively change ownership of the directory .../webapps/jasperserver/
. Or you might prefer to only chown .../webapps/jasperserver/WEB-INF/attachments
. Or you could change the attachments directory by editing this line in server-config.wsdd:
<parameter name="attachments.Directory" value="attachments"/>