Have a look at Survey123 for ArcGIS: https://survey123.arcgis.com/

Easy to configure and integrates nicely with ArcGIS Online.

Very nice but... all users must have an arcgis online account, so very restrictive

I've been looking at this in terms of QR codes. I haven't tried it yet (I plan to give it a go shortly) but something like this (https://qrd.by/) will let you scan a QR code and send it to an address including the coordinate at which it was captured. The address could be a workspace on FME Server that generates a HTML form to be filled in and submitted.

The form to be filled in could include a field for a file upload - in this case a photo. So the user could:

1. Take a photo
2. Scan a QR code (they could just have it on a piece of paper)
3. The code sends a coordinate and opens up a form
4. The form allows upload of the photo

It's a bit hacky I know, but it could work. I also found a QR code app called pic2shop which can be used to send coordinates (needs the pro version) but also is a solid base tool for building your own QR code tools.

Actually, now I think about it, it doesn't even need QR codes if the photo is geotagged. Just visit an FME Server URL that generates a form. Upload the photo in the form. Have FME process the form and generate the coordinate by extracting it from the geotagged photo's exif info. Pretty simple and just needs a bookmarked URL, not even an app.

And if the photo isn't geotagged, FME Server could open up a web map interface to allow the user to pick a coordinate/location off the map directly (or even open it anyway to allow fine-tuning of the photo location).

Hope this helps. I'm planning to do something similar (if I get the time) in the near future since I think it would be useful demo. Keep an eye on the FME blog, since that's where I'll describe the project if I do.

Here is an example that might be useful: