I have a folder with images that updates every five minutes (screenshot from other programs). Is it possible to automatically transfer these images to screenly everytime that the images updates? Or is it possible for screenly to fetch them somehow?
You will be on your own if you really want to try and do this, but if so, you will need to use the API (/api/v1/file_asset to be specific): http://ip.of.your.pi/api/docs
And, will need to create your own script that is always running and using the API commands with curl and since you wont have unlimited storage you will also need to create as part of the script the line that deletes the already uploaded assets.
There is no automatic sync between a directory.
Could you maybe record yourself using a web automation program/tool to perform these actions for you on the web GUI? Possibly.
Do I see it working the way I think you want this to work? Nope.
Screenly/Anthias does not fetch in the way that you are trying to imagine it does.