Upload is preferred. That should (but not necessarily MVP) include the ability to paste a URL and let Codidact pull the image from elsewhere. While conceptually that may seem the same as “link to extant images”, it is not. Link to extant images (i.e., a link that displays an image here) has several problems:
- Links break over time due to content elsewhere changing URLs or web sites disappearing - all beyond our control.
- Actually allowing user-entered <img> links raises a host of security issues.
- Storing the images locally allows us to make sure the images are truly images (i.e., match a normal JPG or PNG or GIF file format).
Storing images locally (whether collected via link paste or a true upload) has the one disadvantage of leaving the site open to copyright issues. However, that is really not a big deal - as with text content, if there is a reasonable request (however that is defined) to remove, we remove it and notify the user who can challenge, etc. But it has the big advantages (over links-to-user-supplied-sites or to SE-style hosted-for-us-elsewhere) of keeping the system reasonably self-contained and not reliant on other sites for primary content.