In your custom ImageFile, implement override Thumbnail method to provide your own logic instead of Optimizely making the assumption there's a generated thumbnail in the primary blob storage.

public override Blob Thumbnail

Thank you for your answer.

There was a typo in my original post, it was 403 error not a 404 error. Apologies for that.

Although I have tried your suggestion,  The thumbnail url seems to be the same, even after adding custom logic, 

I have debugged with this sample code, seems Thumbnail url is correct one, but episerver is loading with main image.

Some more detail:

1. I can see image with this url  https://***.***.com/3176ddd00b72438da42c14783466b5b0/67b8047c1ebd4edba2e96e710fe11200.jpg

2. Thumbnail with:  https://***.***.com/3176ddd00b72438da42c14783466b5b0/67b8047c1ebd4edba2e96e710fe11200_Thumbnail.png

But episerver loading the url with https://***.***.com/3176ddd00b72438da42c14783466b5b0/67b8047c1ebd4edba2e96e710fe11200.jpg/Thumbnail?epieditmode=False?1659371043774 which seems giving me 403 error

Hi Neelam Yangal,

  I am also facing the same issue. I am not sure why the extra integer digit is appending with the thumbinal url .

   If you are able to resolve the issue. Can you please help me ?

late to the party, is your S3 configured to block certain IP?

Hi Quan Mai

I am not loading the image from s3 bucket. I am loading image from external json that contains image thumbinal url . I am not sure why it's appending the extra integer digit for all the thumbinal url. We are not adding anywhere in the code.

It looks like your issue is different than what I was experiencing. But in my case, while registering the route at global.asax.cs, I have changed the image virtual path. If images have blobs, then change the virtual path to the CDN URL + Blobs URL. HTTPS://***.***.com/3176ddd00b72438da42c14783466b5b0/67b8047c1ebd4edba2e96e710fe11200.jpg

So this change (CDN URL + Blobs URL) has broken my thumbnail URL and it was not loading the images. But in our case, we have two servers client-server and an admin server. On the admin server, I am not converting the image URL to the blobs one, so this has solved my issue. The client-server continues to deliver images from CDN.