Graphics are imbedded in RTF in either a binary format or an (ASCII) hex dump of that binary. I have never seen a binary format graphic - I don't think that the filter will process binary correctly. It does handle the hex format of graphics, by converting the hex back into binary and writing the binary to a file. The file extension is chosen by looking at the original type of the graphic. The following list shows the file types and their extensions:
In addition, the filter produces a link to the file containing the graphic. Now, since the above graphic formats are not very portable, the filter assumes that you will convert these files to something more useful, like GIF. So the format of the link is:
<a href="basenameN.ext">Click here for a Picture</a>
There is one other special case. If a graphic is encountered when the filter is in the process of generating a link, the IMG form of the link is used even without the -I command line option.