Full rules here but this is the meat.
" Only minor Photoshop work should be performed in the field.
(Especially from laptops). We require only cropping, sizing and levels with resolution set to 300dpi. Where possible, ask your regional or global picture desks to perform any required further Photo-shopping on their calibrated hi-resolution screens. This typically entails lightening/darkening, sharpening, removal
of dust and basic colour correction."
I put this up in the PJ section but got to thinking others might be interested in seeing what a profession photo outlet such as Reuters is now asking of those submitting.