How to organize ASP.NET request locking or row locking in DB

I've asp.net page/handler to access images. When performed fist request to the image I resize image to standard size(save on disk) and return it. So I need lock all request to the image except one. This one will resize image. Image identified by 开发者_如何学编程ID in URL, so I guess one lock object required per one image(ID in URL). My question is How can I organize this lock model?

My idea add lock object in Application (Application is synchronized) like this Application.Add(Request[Id], new object()); and use it to locking competitive threads.

This task like row locking of DB or locking element in collection.

Thanks for your replay.

The easiest way is locking image file with.

using (FileStream fs = new FileStream("image.file", FileMode.Create, FileAccess.Write, FileShare.None))
{

resize image here 

}

When second(third etc) thread try to create file the Exception "The process cannot access the file ..." will throw. And I process this exception in code.