If you read this post, you probably have a client computer where the html mail in Outlook 2003 shows a red x where either the picture is a link or embedded in the mail. A number of web sites has the solution if we’re talking about the embedded pictures. You could then probably follow the instructions for deleting the registry key for the OutlookSecureTemp folder referenced in http://support.microsoft.com/default.aspx/kb/817878 or clean out the folder manually.
If your problem is related to images that are link to an Internet URL, you should check your IE settings. Where I work, we use a transparent proxy, so IE is set to detect settings automatically. This is accomplished with WPAD so you don’t have to to anything on the client. What I’ve found out is that Outlook is unable to detect this setting on a couple of clients, but if you insert the proxy address manually in the Intenret settings the picture link works. IE itself works flawless.
Haven’t found anything on the Microsoft KB concerning this, but seems to be a bug in the Outlook 2003 software. If you have any idea what could cause this feel free to post it.