The book is packed with mistakes. It can't go well for a book when the author doesn't even know how to pronounce the last names of his two main subjects. "Liddell" (Alice's last name) rhymes with "riddle," and is not pronounced with an accent on the last syllable. Carroll puns on the name sounding like "little" in at least two places in Wonderland. Winchester pronounces the name wrong in the video on this site, and, if I hear correctly, he pronounces Dodgson (Carroll's real last name) wrong as well. Carroll did not pronounce the g; it was pronounced "DODson." He states that Princeton owns the only two copies of the photograph. This is not true. He is misinterpreting Edward Wakeling's recreation of Carroll's photographic Register, a list of all of Carroll's photographs. Wakeling says he is only listing one location even if there are more locations for a photograph. Winchester has Carroll living in his final rooms at Christ Church throughout his entire life at Oxford. Carroll moved around several times and was not in his famous rooms even when he wrote Wonderland, well after he took the photograph of Alice as the Beggar Maid. Winchester doesn't realize that two pennames that Carroll submitted to an editor are anagrams of "Charles Lutwridge" (Lutwidge was his middle name and mother's last name). Winchester writes that the photographic plate must be prepared in "pitch dark" but later in the book writes in "near-total darkness." I believe the latter is correct.
Winchester does not understand how a view camera works. He writes that the whole of the camera needs to be brought into the darkroom for the plate to be inserted. But he writes that there is an "ingenious flap" and so only the negative frame need be brought back in the darkroom for development. I believe, and someone please correct me if I am wrong, that the whole of the camera need never be brought in the darkroom. He also has Carroll under the "black velvet shroud" while the plate is in the camera. Of course, once the plate is in you cannot see anything at the back of the camera anymore, it is blocked. He also has things out of order, the subject and picture are all arranged before the photographer prepares the plate, not after. This comes off especially bad for Winchester because these errors take place while he is fictionalizing two photographic sessions, which naturally make the fictionalizing much worse.
It is true that Carroll noted in his diary the number of boat trips Ina, Alice's older sister, took at one point. But he uses this out of context. It is also true that Carroll marked one day with a "White Stone" (a way he marked special days in his diary) when Alice was about. But this is also used out of context, as if it only refers to Alice.
He writes that exposure times could be as long as 45 seconds, a common statement in papers on Lewis Carroll, to be honest. But this is like saying a baseball team can score as many as 23 runs in one ballgame to someone who doesn't know anything about the game. It says nothing about the norm. Carroll is on record as taking one at 90 seconds and 45 seconds and 10 seconds. The first two, however, are mentioned because they are long and outrageous. Winchester writes that "neck braces and tie-downs" (to hold sitters in position) were not used in the wet-plate process. Not true. Braces, or head-rests were used and you can see a head-rest in many (5 or 6?) of Carroll's photographs. Carroll even mentions buying a "head-rest" as late as 1876. And of course, you can see head-rests in the illustrations for a poem Carroll wrote about a photographer ("Hiawatha's Photographing), which Winchester himself mentions and quotes.
Winchester gives Duckworth's account of how Alice asked Carroll to write out the story the day of the trip and that Carroll began writing, in part, that night. Winchester even has Carroll writing it out as we see it today in facsimile. But Duckworth's account (he was the other adult on the boat that famous day) goes against Carroll's diaries and Alice's account that she gave later in her life (without the knowledge of Carroll's diary). Carroll and the older Alice have the younger Alice asking the next day (when they met at a train station) and Carroll writing them out on the train to London. Winchester does write "According to Duckworth" but clearly it should not even be brought up, being obviously a romanticized account.
Winchester says Under Ground is 15,500 words (it is 12, 772 or so) and that Wonderland is almost double (it is more than double). He says that Alice naming her son "Caryl" was "her only public acknowledgment of her connection." But I've always read that she denied this.
It is the nature of photography that we hardly ever see the actual photographs but see reprints only. His bit about this photo being rarely seen in the library at Princeton makes for an ineffective framing device. (He opens and closes the book with this idea.) Also, he loses points because it is not only at Princeton as he writes, as mentioned above. He wants that Da Vinci Code mystique of having a rare document, writing "consigned to the secure and deep darkness of the Firestone Library." But it doesn't work here at all.