Hi there - sorry for my slow reply - it depends on the use and on the work!
If my work is to be used as reference (i.e. not manipulated/combined with/in the derivative work or pasted in a work, but instead redrawn/used as pose reference etc) then I'm usually happy for it to be used for commercial works - but best to ask me about which photos you wish to use and specify how!
If it's to be manipulated or combined with/in the derivative work or pasted in a work then I can't grant permission for some photos as they were taken at sites where the rules prohibit commercial use - some of the other photos I can grant permission (the ones of my own cats or friends cats, for example) but I'll decide on a case-by-case basis.
I hope that's of help - send me a private message if you have any further questions or wanted to discuss use of a photo a bit more!