Best practice approach - Writing captured graphic file to a server

I've received very useful help from this forum, for which I'm grateful. I have a prototype app. which is operational in every respect, other than transferring files below from the device to a server, to enable office staff to be able to pick them up:

1. Small line of captured text.
2. A captured signature PNG file.
3. An optional JPG image file.

I've looked into Restful services and JSON. Up to now, for loading data into my prototype, I've developed my own method by reading content from pages on our hosted web server, using httpClient.GetStringAsync(" "). I designed the protocol for this, but in time I'll no doubt re-develop it, although it works fine.

I can't use this approach for getting the above 3 items back to a server and I'm unfamiliar in regard to what might be the best practice. I've been reviewing some samples such as this recent one on the forum, which uses client.PostAsync(url, content) Unfortunately it points to a broken link.

Would I be correct in thinking we'd need to write our own code at the server end, for instance in PHP, to capture this POST data? Or is there a simpler way (or an existing way) that can make use of common services within popular hosting plans, such as MySQL etc? We don't really need to do anything especially sophisticated with this data, just that it needs to be accessible in some way. Thanks for any suggestions.