Proved - proven
Proved and proven are alternative forms of the past participle of Prove (irregular verb)'. (As a point of etymological precision, it should be noted that the Latin word probare came to English through French in two forms: the southern was 'prove', with a past tense and -ed participle proved. The northern form was preve, which may still be heard in Scotland; and the past form proven belongs to that.) OED in a draft revision of its article in 2008 said that proven "...is the usual form in Scottish English (as opposed to PROVED adj.), and also the preferred form in current North American English. It is now also more frequent than PROVED adj. in British English."
So the choice of which participle or adjective to use is a matter of personal choice in most contexts. Proven may feel more formal to many native speakers of British English. In one context it is obligatory to use proven - in Scots law, especially with the verdict in criminal law, 'Not Proven'. (This is a verdict where an accused has not been able to prove innocence, but the prosecution cannot prove guilt. As a judge is supposed to have said, "You leave this court a free man, but with a stain upon your character." Scots who defend this verdict often point out that in England, a person found 'Not Guilty' usually has a similar stain on the character; in Scotland, 'Not Guilty' should be seen as 'Innocent' much more easily.)
You may note when seeking to choose between proved and proven that proven is now the more common word. Always choose proved as the past tense.
Although speakers in southern England pronounce the vowel of proven like that of 'proved', with a long '-oo-' sound (IPA: /ˈpruː vən/), the traditional pronunciation in Scotland, approved of by Burchfield's Fowler, uses the vowel of 'over' in the first syllable, IPA: /ˈprəʊ vən/: LPD on the other hand records IPA: /ˈpruː vən/ as the commoner pronunciation, with /ˈprəʊ vən/ as only a secondary realization.