Beginner – ASP.NET Core – How do you deal with images and similar media in a back end?

I’m new to back end programming with ASP.NET. I’m wondering how to deal images that are either taken with the users camera or just uploaded with their gallery. At the moment I have a nice little ‘DeliveryItem’ object with things like Strings for name and Ints for quantity and all that, but essentially what I want now is public image ItemImage { get; set; }.

‘Cannot Access a closed file’ error on some files

I’m getting Cannot Access a closed file on some files when I try to upload them. I’m creating a small web app, when a user creates an account on the website, they are required to upload a file. Once they have uploaded the file, I should see it in MongoDB. The issue is some files are uploaded successfully while others create errors. This is the exact error msg from the log:

Postback Request of ASP.NET Controls are taking too much time

I have created an asp.net website http://www.oureasymart.com which is working fine In localhost. but after hosting it to godaddy when an asp.net control like button is clicked then it is taking too much time around 1 minute to perform its operation. This problem is for every asp.net control of each page.
I think there is no issue with code behind or click event because I tried a simple Response.Redirect() method to move to next page on click of that button but still it is taking same time. Also I tried to call same method with the help of Jquery Ajax and it is working fine. I also enabled tracing in which I checked there is no event which is taking even 1 second. Please have a look at the code and screenshot of trace info and suggest what may be the issue.
TRACE INFO : https://drive.google.com/file/d/19Cl6wpe_Y20FCzxI9d0bUvj8BdaUdgjR/view?usp=drivesdk