In case you haven’t resolved this one yet, I’d suggest using a packet sniffer or CURL to see what is going on (provided you are not testing a localhost connection). Browsers (by design) have a pesky habit of caching images, so in cases like this you can’t always be sure what you are looking at (or not) in the browser is what is currently being delivered by the server. Wireshark (http://www.wireshark.org/download.html) is my current tool of choice but any other packet sniffer would also work. While there are easier ways to ways to verify what content is being sent from the server (such as the Firebug browser add-on or the CURL command line util) I prefer a packet sniffer because that’s just what I’m used to using from my client/server app development days. Other HTTP request monitoring tools may work better for you.
Once you’ve verified that the content is either being delivered or not (Fedora XACML policy in place preventing direct access except by localhost?) then you can move on to verifying if you browser (or more than one) can correctly interpret the TN image data.
From: Josh Wilson [mailto:email@example.com]
Sent: Friday, April 26, 2013 5:08 PM
Subject: [fcrepo-user] Issue with TN datastream/PNG images
I'm working on an Islandora install, using Fedora 3.5, on a Windows IIS7 server.
I've been having an ongoing issue with getting Islandora running, but I think I've traced the problem back to something specific with Fedora. Fedora doesn't seem to be able to view the TN datastream (a thumbnail PNG image that Islandora uses). If I browse around in Fedora, I can view all Islandora datastreams except for the TN, which for islandora:root is a folder PNG. When I try to see that in the browser (i.e., http://[ip redacted]:8080/fedora35/objects/islandora:root/datastreams/TN/content) I get an error in Firefox (in IE, I just get the broken image box with a red X):
'The image “http://[ip redacted]:8080/fedora35/objects/islandora:root/datastreams/TN/content” cannot be displayed because it contains errors.'
I know this sort of error can have a lot of causes. I've personally seen something like it when I was working with some images that had been saved with a CMYK color scheme. But in this case it seems that the image is either being truncated or there's some other configuration problem with Fedora which prevents it from being served. I'm pretty new to Fedora and unfortunately I don't know how to go about diagnosing the problem in further detail or fixing it. Any suggestions?
Some additional observations:
--Nothing shows up in the Fedora or Tomcat logs when this error occurs.
--I can see the image fine if I don't go through Fedora, i.e., http://[site name]/[path to image]/folder.png
--I thought perhaps there was some PNG-specific issue, so I tried embedding the folder image into a Tomcat page ($CATALINA_HOME/webapps/ROOT/index.html), but when I go to localhost:8080 it shows up.
Thanks for any help.