I guess we'll find out in due time how accurate these pics are...The exact source and date of this picture is unknown to GMI, though our sources adamantly claimed it to be authentic. We tend to believe this given the facts listed on the sheet along with the pictures. Also note, that the picture appears to be a scan of a photocopied version of the original document (say that three times fast!), leaving graininess that makes this a unlikely candidate for any photoshopping tricks. However we must keep in mind that in our high-tech world anything is possible. Interestingly, there are no copyrights or internal markings that would designate it's source anywhere on the document.
Another item pointing towards the authenticity of the pictures is that in comparison to the the spy pictures released on other sites the cars proportions seem to match up exactly. Adding to the mix, even the wheels seem to be very similar. Remember the STS being based on the Sigma chassis is essentially an enlarged CTS, however it will wear all new panels. This is illustrated by comparing the highlighted body panel in the picture immediately above to this spy picture of the STS . This body line is very similar on the two STS pictures, but very different on the Cadillac CTS. This alone is a very strong factor in proving the documents validity.
The only alarm on this picture is that the documentation lists the car as "Seville", and not "STS", which is the name we are all hearing. Though at first this is worrisome, remember that GM referred to the CTS as "Catera" for a while before its launch and at it's root CTS does stand for "Catera Touring Sedan". The same is true of "STS" which stands for "Seville Touring Sedan" and has so for a while. Either way GM has yet to publicly refer to the Seville replacement as "STS", so it is entirely possible for them to refer to the car as Seville until it's new name is official.
One last thing to remember is that the age of this document is unknown, and about a year ago Bob Lutz ordered the STS to have a slight redesign. It is unknown if our document is representative of that change or not. There is a lot of Cadillac Sixteen in the rear which points to it being the new design, however muddying the waters, the front is pure CTS Art & Science. It is known that Lutz is a had a huge hand in the design of the Cadillac Sixteen, so much so that the new styling treatment is jokingly called Art & Bob at GM. Judging by the other spy pictures, if there were any changes from this design they were small changes in the front and rear. Either way take the details of the picture with a grain of salt.