My scenario
I will get logged into to SSO through Adapters and fetch some data and then need to get the image and show in the app.
To access the Image you need to login and then you can access.
I had already logged in this SSO for fetching other data through adapters
So My Question is
Do I need download the image through adapter only.
or Can I directly use tag and give the URL as src.
What does the display of an image has to do with SSO? These are two distinct and different things.
Additionally, your scenario is very scarce of details... you need to edit the question and elaborate to get a more complete answer.
Anyway...
You can do either one of the options you've mentioned: get an image file & display it and using a URL to an image.
If you intend on using an image file, you will have to first make sure the image you will fetch is base64 encoded and then get the resulting string in the adapter response. To display it, you will then need to base64 decode it and display it.
More on base64 encode/decode
post image using worklight http adapter proper format
If you intend on using a URL to an image, you will have to simply place the URL (which is the adapter response) in the img tag.
You could also use the Cordova File Transfer API to fetch images, store them locally and display them.