Numismatic Guaranty Corporation has been offering Third Party Grading of ancient coins for six years. Usually the company slabs the coins. I recently acquired two NGC-graded ancients that couldn't be slabbed. They came with laminated Photo Certificates.
The certificates are huge: 195mm x 120mm. I don't collect anything else this size and had no idea how to store the certificates with the coins. I finally found Supersafe 2 Pocket pages for Graded Currency which hold them and integrate well with a collection stored in a three-ring binder. Unfortunately these 2 Pocket pages don't have any kind of clasp or door and I will be nervous traveling with certificates in this kind of container.
Although the certificates are huge my smaller coin, a 1/64th stater weighing 0.14g, is exceptionally tiny. This coin is supposedly on good metal, with surfaces graded 4/5 by NGC, but blown up to the vast size of the photo certificate it looks painfully rough. I would have preferred a baseball-card sized photo certificate that could be stored in a safety deposit box. (If I had very large coins I expect large photo certificates, and it does make sense to standardize on a size. Just note that tiny coins that look good in hand may appear hideous when 6mm is blown up to 70mm).
As far as I can tell from the web site, photo certificates are only available for coins NGC is unwilling to slab. The web site authors seem not to have considered collectors who prefer the flexibility of certificates over the finality of slabs. I have no clue if it is possible to request only the certificate.
Each coin is given a unique serial number. Entering the number into a form on NGC's web site brings up photographs of the coin and the certificate. For example, my 1/64 stater can be seen at http://www.ngccoin.com/certlookup/index.aspx?CertNumber=2412827-016. This part of NGC's web site seems poor. There is no population data. The 'Pedigree' listed for my coin is 'rv eagle head r.', which is of course the reverse description, not the pedigree. (So far I have been unable to trace the pedigree of this particular coin myself beyond the auction I purchased it in.)
Laminated with the photograph is a hologram and a 'photo-certificate.' I would have expected the certificate to be intaglio printed but it looks computer printed.
The 1/64 stater came with tiny slip of paper saying 'NGC has not certified this coin' because of 'other' with 'size' written by hand. This paper is wrong: the coin was certified by NGC. The certificate team seems to lack slips saying 'NGC has not encapsulated this coin' and is repurposing 'reject' slips.
My other photo-certified coin, a plated obol, should be visible at http://www.ngccoin.com/certlookup/index.aspx?CertNumber=2412832-011 but it seems NGC did not upload the picture. The plated obol's photo-certificate includes the annotation 'ancient forgery' and this important information is not present on the verification page. I was happily surprised to learn the ancient counterfeits can be certified, as the web site claims 'NGC Ancients will only grade coins it believes to be genuine.' Leaving the forgery annotation off the web verification page seems like a major omission. It is also confusing to have a certificate that says 'ancient forgery' on one side and 'genuine, original' on the other, even though all serious collectors will understand what is meant.
I have been impressed with NGC's creation of the numerical ratings for Strike and Surface as distinct from wear grade. Acquiring a few NGC-graded coins changed the way I think about a coin's condition. Although I still struggle to understand all the nuances of 'Surface' I find NGC does a good job grading ancient coins.
It is unfortunate the industry hasn't come up with a reclosable slab yet, but NGC's photo certificate has a lot of potential until such a slab is invented.