Editing photographs in paper When using photographs for papers (assuming they've been taking by the author), to what extent can they be retouched and (a) be used without mention of retouching or (b) used but require mention of retouching?

I imagine that levels adjustment and cropping would generally fall under (a), but other types of processing give me more pause.  For instance, while stitching photographs together seems innocuous enough, it often necessarily involves interpolation.  And if some interpolation is acceptable, where would the line be drawn?  Power lines in front of a building or dust/scratches on older photographers seem like they'd be okay, but restoring a larger block area seems more dubious.

To what extent might these practices vary by field?  (I imagine astronomy and architecture probably have quite different standard practices)
As far as I'm concerned, if you're using someone else's photograph and you don't have a clear set of rules stating that you can edit it i would avoid doing so, unless it's a very, very basic thing, like cropping it to hide the cars. 

You could also use the legend box commonly written below the picture to help explain it, for example: "Recent picture of a church constructed on the XII century." 

If the visual aspect of the church is really important to you could try to recreate how it would look when it was recently constructed (maybe pay a designer to do so) and make it your own thing (of course, referencing the original author: "Recreation of what the church of bla bla bla would look like on the XII century. The original picture was taken by XXXXXX and treated using (...)"