Hi Talvinder,
Apologies for the delayed response. Thanks for sharing that extra info.
I setup a similar use case and saw the same thing i.e. Bot > Send an Image just returns the word ‘image’ in Slack. We may need to look into why it behaves this way but sometimes it’s just a case of different platforms reacting in different ways to our services 
What does seem to work is using Bot > Send a Message and just including the captured URL - Slack will load up the image for the user.
Please can you give the send a message action a try and let me know if you run into any problems with it? 
Edit: I’ve just noticed that you also mentioned the private file URL as an issue. I’m not sure if there’s a way to change the default capture behaviour in Slack so that the sent file is set to public. I’ll look into this and update back on here once I find something.
Thanks,
Dan