Mould tool use

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I took some pics of much of my dad's art collection, hoping to help advertise them for sale. To avoid glass reflections, I shot them all at an angle, thinking that it wouldn't be a big deal to correct the trapezoidal distortion. I can't, however, seem to get the barrel distortion to totally go away. If any of you have any helpful techniques that you'd like to share, it would be greatly appreciated. Thanks.