Download and convert to base64 remote images

Hi there,

I need to have part my app working offline. This part include pictures.
As far as I can see, there are two options :
1 - on my server-side I convert pictures to base64 send them that way (or make them available to be downloaded).
2 - on my app, I request the pictures via their URLs and convert them to base64 locally

What’s the best approach ? Is downloading a file or downloading its base64 representation the same thing ?
I haven’t been able to find anything for the option #2. Any suggestions ?