I have a c# function for producing thumbnail images, these images are displayed on web-page i.e ASP.net So how would i programtically call this back-end function let say eve
Either write a windows service or schedule a job.
Write your code as a standalone console application - and then set up a scheduled task on the server to run your application at this time everyday.
If you want the task to run more than once a day you will have to set up a scheduled task for each time.
To set a scheduled task up go to Control Panel > Scheduled Tasks and then click on "Add Scheduled Task". This opens a wizard which guides you through the process:
Then you are done.
You can tweak the settings once it's set up.
Another way to handle it is by using Quartz.NET. It's pretty powerful job-scheduling library. This answer talks about using it with asp.net.