Viewing pictures posted in threads

[fullfan]

Is there a reason when in most threads I read that when someone posts a picture all I can see is a box with an "X" in it?  In the Hunting and Fishing forum for instance someone will post pics of a turkey or fish or whatever and others will reply nice bird and all I see is the "X".   I know its something simple but I'll admit to not being that tech savvy.

Thanks for any help.