How can I find the value of a painting of Pinkie?

Answer 1

Both 'Pinkie' and 'The Blue Boy' are part of the permanent collection of the Huntington Library Museum and aren't for sale. Even if 'Pinkie' were for sale the price tag would fetch many millions, certainly at least 25 million.

However, there are websites like this one:

http://www.artchive.com/ftp_site.htm

where you can buy prints of this painting or other famous works.

If you're asking about another artist's copy of the original portrait how much if would be worth, as a copy of an original, would depend on who painted the copy (it could have been made by an artist who became famous later) and how well the copy was done. However, copies of original famous paintings are rarely worth a lot of money.