To politely ask your best friend to stop sending you excessive pictures without hurting their feelings, you can start by expressing your gratitude for their friendship and their willingness to share their experiences with you. You can then explain that you have been feeling overwhelmed with the amount of pictures you receive and that it has become a source of annoyance for you. It's important to be honest and direct with your friend, while also being respectful and empathetic towards their feelings.
You can also suggest alternative ways of staying connected, such as scheduling regular phone calls or video chats, or setting up a shared photo album where you can both contribute pictures at your own pace. By showing that you value your friendship and are willing to work together to find a solution that works for both of you, you can help your friend understand your perspective and avoid hurting their feelings in the process.