This is a feature for Commons_media datatype on Wikidata.org:
Feature summary (what you would like to be able to do):
If a Commons file has several pages (e.g. a djvu or pdf), the thumbnail is currently generated from page 1. This can be relevant or just a mostly blank cover sheet.
Sample: https://www.wikidata.org/wiki/Q75803176#P996
Wikidata uses the qualifier "file page" number (P7668) to indicate which page should be displayed. There is also the qualifier "title page number" (P4714) for other cases. If both are present, P7668 should be used.
Steps to reproduce (a list of clear steps to create the situation that made you report this, including full links if applicable):
Sample with "file page" number (P7668) qualifier:
- Go to https://www.wikidata.org/wiki/Q75803176#P996 that has the qualifier P7668 with value 160
- https://commons.wikimedia.org/w/index.php?title=File:Emily_Dickinson_Poems_(1890).djvu&page=1 is displayed
- Expected: https://commons.wikimedia.org/w/index.php?title=File:Emily_Dickinson_Poems_(1890).djvu&page=160
Sample with "title page number" (P4714) qualifier:
- Go to https://https://www.wikidata.org/wiki/Q43431543#P996 that has the qualifier P4714 with value 9
- https://commons.wikimedia.org/w/index.php?title=File:Boccaccio_-_Il_Decameron_I,_1877.djvu&page=1 is displayed
- Expected: https://commons.wikimedia.org/w/index.php?title=File:Boccaccio_-_Il_Decameron_I,_1877.djvu&page=9
Uses (as of August 2021):
- 2392 uses of "title page number" (see https://www.wikidata.org/wiki/Property_talk:P4714 )
- 7307 uses of "file page" number (see https://www.wikidata.org/wiki/Property_talk:P7668 )