How to extract the differences in two almost identical pics?

Does anyone know can two almost identical images differences somehow extracted to a new layer ( with eg photoshop )
For example photo without any unnecessary marks:

the exactly same photo but with disturbing “dirt”

any help would be appreciated.
Answer #1
Sorry i cant see any “Disturbing Dirt”
Answer #2
well this might work – drop each into their own layer, and set the blending mode of the top layer to difference. any differences will show up right away, but they’ll be the wrong color. just use the results to build an alpha mask, which you can then use to separate differences into a new layer. shouldn’t be too tough
Answer #3
Sorry i cant see any "Disturbing Dirt"
what I mean’t to say how remove that ugly square ~ I am a Potty Mouth ~ that’s ruining a beautiful picture
well this might work - drop each into their own layer, and set the blending mode of the top layer to difference. any differences will show up right away, but they'll be the wrong color. just use the results to build an alpha mask, which you can then use to separate differences into a new layer. shouldn't be too tough
Thank you for helping me, I think I managed to follow the instructions with a satisfying result.