Hi,
Two other possibles.
Check the Contacts App > Card Menu > Show the My Card
Is this your details ?
In Finder window hold down the ALT Key whilst selecting the Go Menu.
Select the Library that appears (you are in ~/Library which is normally hidden)
Navigate to Caches/com.apple.Messages/Pictures
This should display all the Buddy Pics for all your Buddies (mainly AIM and Jabber ones)
If one of these is corrupt then it can effect the app.
Like this one for instance

The pic does not display in this view and the size id Zero bytes.
Others may look odd in other views

This is less of a problem in later version of Messages compared to iChat but it is worth checking.

9:58 pm Thursday; June 16, 2016
iMac 2.5Ghz i5 2011 (El Capitan)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone and an iPad (2)