188.8.131.52.1.1 Inline Attachments in RTF Messages
If the best body text format is RTF, MIME writers SHOULD<78> treat all OLE attachments, and only OLE attachments, as inline attachments. OLE attachments have 0x00000006 for the value of the PidTagAttachMethod property ([MS-OXCMSG] section 184.108.40.206).
RTF text does not contain explicit references to inline attachments, as HTML text does. Instead, the position of an inline attachment in the RTF text is indicated by an \objattph control word; clients insert such a tag into the RTF text for each inline attachment, as specified in [MS-OXRTFEX]. Clients also set the value of the PidTagRenderingPosition property ([MS-OXCMSG] section 220.127.116.11) to indicate the order of inline attachments: the attachment with the lowest value of this property matches the first \objattph control word; the next lowest matches the second \objattph control word, and so on. MIME writers sort inline attachments by the value of the PidTagRenderingPosition property when converting RTF text with inline attachments to HTML, and insert an HTML IMG element into the generated HTML at the position corresponding to the RTF \objattph control word.