Why does the HCMPERSONIMAGE "Image" field have an extra 7 bytes? Does BinData add some extra information?

I am trying to extract the person image from the HCMPERSONIMAGE table directly via SQL.  What I have found though is that I need to strip the first 7 bytes from the resulting binary file in order extract the original image file.  My assumption is that BinData is used to write that binary image to the database?  If so, what is BinData adding to the beginning of the file?  

Thanks for any input anyone can provide.