Based on current research, in the period 1870–1900, the most prolific commercial studios that published albums of large-format souvenir photographs were those belonging to Émile Gsell, Pierre Dieulefils, Aurélien Pestel and Raphael Moreau. The studios of Dieulefils and Moreau helpfully included numbers and captions in many of their negatives and this information can be seen on the face of the prints. Pestel did not do this but instead gave handwritten captions, without numbers, on the album pages.

Gsell, on the other hand, was inconsistent in the way he provided such data. In his early prints of Angkor Wat, Cambodia, he usually signed his name in the negative and included a number. Exactly when he began to do this is not entirely clear but it is likely to have been around 1870. Before this, explanatory captions with corresponding numbers were shown separately on small printed labels pasted beneath the images. In almost all of his non-Angkor Wat photographs, both Cambodian and Vietnamese, he neither included his name nor a number. Instead, his studio provided handwritten captions on the album pages. In the mid-1870s, however, he started to add numbers to the negatives.

In the case of Gsell's cartes de visite, numbers were often, but not always, included on the face of the prints or the reverse of the mount together with handwritten captions. If the cartes were pasted onto album pages, then the captions would appear next to the images, with or without numbers. Very many of Gsell's cartes de visite were also published in large format.

The presence of captions or numbers is an essential aid in identifying a photographer's work. Despite their incompleteness, researchers should find the following number lists for Gsell and Moreau helpful. The numbers for Dieulefils have not been included although it is not too difficult to identify his albums by comparing their images with those shown on his literally thousands of postcards.

In the author's experience, the inadvertent conflation of the works of Pestel and Moreau is a significant impediment to the accurate attribution of nineteenth-century photographs of Vietnam. The number list for Moreau, shown below, should be of assistance in helping to resolve this problem.