Umm,
They were things that I have used during the time I have had the issue myself.
It seems to have improved things on some services (namely AIM) but have left the issue the same with my Bonjour connection to my Snow Leopard Mac.
On mine the File Transfer window reports it Failed (See Window Menu).
On other accounts sometimes the Chat shows an icon and it will open in Preview rather than displaying In-line.
It is not something that I do that often and is not something I have spent a great amount of time on.
You could try this:-
In the Finder use the Go Menu > Go to Folder and type (or Copy from here) ~/Library/Preferences into the dialogue box that appears.
Once in the Preferences folder find the com.apple.ichat.plist file
Depending on the service the picture is coming on you can delete (Drag to Trash) the Preferences (.plist file) for that service (com.apple.ichat.AIM.plist or com.apple.ichat.Jabber.plist for instance).
There is a Yahoo one and a Subnet one for the Bonjour Account.
Restart the app each time.
If that does not work try deleting the com.apple.ichat.plist itself.
DO NOT delete them together as this will cause the app to have to be reset with the basic account info.
If it is the iMessages account that is effected try deleting com.apple.imessages.bag.plist as this one is the contact with the server as are the ones above.
Again restart the app.

9:14 pm Friday; October 17, 2014
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad