Thank you in advance if you've gone out of your way to take a photo for me. Please bear with me if you do. Sometimes I have no access to my email for weeks due to travel/work that takes me out of internet/mobile phone reception zones. I will thank you personally as soon as I am back.
No immediate reply does not mean I'm ungrateful, simply that I have not yet seen your message.

Thank you in advance if you've gone out of your way to take a photo for me. Please bear with me if you do. Sometimes I have no access to my email for weeks due to travel/work that takes me out of internet/mobile phone reception zones. I will thank you personally as soon as I am back.
No immediate reply does not mean I'm ungrateful, simply that I have not yet seen your message.