For the most part Findagrave has photos of still existing markers and some inscriptions copied from the Hale Collection from those no longer there. The inscriptions copied in the Hale Collection are not complete and include only the "vital statistics." There is a manuscript book at the Middlefield Historical Society in Middlefield which includes complete inscriptions and includes a few photographs, although it does not claim to be complete. The book is Charles Rowland Mills and Frances W. Perkins. Old North Burying Grounds Inscriptions. (Middlefield, 1902). This might include an inscription for a marker which has "gone missing" during the thirry some years between its writing and the Hale Collection.
The Godfrey Library has a complete collection of photographs of all existing (21st century) markers and Hale Collection transcriptions for those which have been lost in the last seventy some years. These are available online for a paid subscription.