You're not.
I assume you're talking about attachments since that is the type of photo that could appear to be blocked. You are blocked from uploading the same image though.
To use an already uploaded image, copy the URL from the properties of the attachment and embed it in a set of [IMG] tags.
The line in your new post will look like this:
[IMG]http://thefiringline.com/forums/attachment.php?attachmentid=12345[/IMG]
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