It's a little bit difficult to answer...
the photographs are from the digital archive of the Szabó Ervin Library of Budapest. It's really difficult to use, and it's only in Hungarian, so I found it better to send many of them directly to this thread.
If you're patient enough to try to see all the 150 digital images online, here1s what to do:
1. go to www.fszek.hu
2. click "adatbázisok" (databases) on the top
3. then click "saját adatbázisok" (own databases) on the left
4. click "Budapest képarchívum" (Budapest Picture Archive) on the left
5. click "Budapest képarchívum" again - on the bottom right (over the image)
these were only the first steps...
6. if you're lucky, you can see the "keresés" (search) window now (it looks really complicated) if you can't click the torch icon in the upper left corner
searching is VERY complicated here - if you're looking for images of the royal palace, the best thing to do is to search it as an "objektum"
7. click to the "index" button in the line of "objektumról"
a new window appears with a list of the "objektum"s (buildings, statues etc.) in alphabetical order
8. find "királyi várpalota" (the easiest way is to write in the words "kiralyi varpalota" or kiralyi next to the "kezdet" (beginning) & then click "keres" (search)
9. if you managed to find the "királyi várpalota" in the list, choose it & click "beír + bezár"
now you're again in the "keresés" window & you can see
"KIRÁLYI VÁRPALOTA ->"
as the searched "objektum" (it would be easy to write it in in step 6, but you can do it only if you've got this character: Á, because the program doesn't understand "KIRALYI VARPALOTA ->"
10. click "keres" (search) (in the bottom left corner)
a new window appears...
11. click "lista" (list) (in the bottom left corner)
FINALLY, a list appears with 151 thumbnail images of the royal palace...
it wasn't that difficult, was it?
I wrote down this complicated process, because finding books about the palace abroad seems to me more difficult. I think they were published only in Hungary, the best ones are:
Hauszmann Alajos, A magyar királyi vár, s. l. [Budapest], 1912 - a great book by architect Alajos Hauszmann with many big, high quality images...
Czagány István, A Budavári Palota és a Szent György téri épületek, Budapest, 1966. - it was published only in 3300 copies...
I don't have any of them... Anyhow, good luck to find some pics/books!!