Although it may be a false positive in this case (Trend is probably matching a specific pattern that appears randomly in the binary content of the picture) this makes you wonder. You can never know if the graphic renderer in WoW is completely safe from specially crafted pictures injected with addons. There are vulnerabilities even in DX9 that could be exploited:
http://nvd.nist.gov/nvd.cfm?cvename=CVE-2006-4183
Not much we can do in that case, just run an up-to-date antivirus with memory scanning and buffer overflow protection if possible
