When you upload a new image which already exists then the old visitor should refresh the browser cache to see it.

C# in Depth, 3rd Edition

To resolve this problem you could each time generate some random number after the image name, and the browser will think that this is a new image and it will refresh it. This is the sample ASP.NET code:

<img src=”<%=YourImage + “?” + RandomNumber.ToString()%>”>