We are building a scanning web app. however, my client doesn't want to install the activex when they using web IE for scanning. does DotTwin Web HTML need to download activex? thank you.

Web deploying DotTwain actually more complex than using ActiveX.  Not only does the assembly have to be downloaded to the client, just as you would an ActiveX control, but the client must setup permissions for your site in the .NET configuration before it will work.

If you create a ClickOnce application it's a bit easier because the permissions are setup for the client, but will not be running in the browser.

Could you please tell me detail steps to create web app for scanning, as I have the similar kind of requirements.