Prevent full size images from downkloading/displaying

Hope I am in the right place to ask this question because I am stuck!!
I have Omeka C 3.1.2 installed and working fine apart from one thing. I am using Derivative Images V2, all my uploaded images are tif files, Derivative images creates me a thumbnail image as a jpg and a postcard size image as a jpg. When I click on a thumbnail image (using Thanks, Roy 2.7.3) I get the postcard size image as a jpg. If I then click on the postcard image I get the full size original tif file downloaded as the browser won’t display it.
What I want is not the tif image but a repeat of the postcard jpg image. I just don’t know where the coding for this is. Can anybody point me to where??
Thank you.

You might want to reconsider uploading tif files, saving them as jpgs (full size) to upload and keeping your tifs as your archive version on your own file storage. Apparently, the base issue may be that, while you can upload tif files to Omeka, browsers may not display them.

Thank you for responding. Yes, I understand tif files can’t be displayed by browsers, that is not the problem. I am using Derivative Images which produces me a postcard size jpg image, when I click on that jpg image it then downloads the original tif file. I don’t want it to do that. I want to change software “somewhere” to just re-display the jpg file.