Hello,
I'm afraid that I don't have any information about the image ad
approval process--I have a feeling there might be different approval
timeframes for different ad types (flash vs. regular image) and
different accounts. If you have an AdWords account representative
assigned to your accounts you might want to ask them, as it's not
something that involves the API.
And no, I don't know of any way of getting back a disapproval reason
for an image ad using v13. The Ad.ApprovalStatus field in v2009 does
expose additional information:
http://code.google.com/apis/adwords/v2009/docs/reference/AdGroupAdService.Ad.ApprovalStatus.html
Cheers,
-Jeff Posnick, AdWords API Team