As no painting has intrinsic worth, its value is arbitrary.
Advanced English Dictionary
+adjective ~ (to sth) belonging to or part of the real nature of sth/sb: the intrinsic value of education + These tasks were repetitive, lengthy and lacking any intrinsic interest. + Small local shops are intrinsic to the town's character. Compare: EXTRINSIC intrinsically adverb: There is nothing intrinsically wrong with the idea (= it is good in itself but there may be outside circumstances which mean it is not suitable).
Random quote: Treat people as if they were what they ought to be and you help them to become what they are capable of being.: Johann Wolfgang von Goethe