1. I think I’ve read a comment explaining that there is a setting for lemmy instance admins which en-/disables stripping metadata when images are uploaded
2. Yes, but it strongly depends on your OS. For windows see https://www.microsoft.com/en-us/microsoft-365-life-hacks/privacy-and-safety/how-to-remove-metadata-from-photos.
3. Essentially no, but it might depend on your setup (i.e. exotic Browser Plugins, School PC with power tripping admin or whatnot)
4. Depends on your setup, but I’d say no. You can look at the meta data (also called exif data) with the method explained in 2
5. Since there are insane dedicated people who deduce locations from the tiniest spek of information (i.e. shadows and a clock), the safe bet would be not to post any photos 😅 But I’d say, remove the meta/exif data and you are probably fine

I’ll add that you can use https://0xacab.org/jvoisin/mat2 as a metadata removal tool, it’s used by Whonix and Tails, and similar distributions. It’s packaged for every Linux distribution if you use that.

There is of course a way to strip metadata from pictures.This is what I use on Android. It is also the way how I upload pictures of my pigeons on this lemmy instance.

On Linux there is exiftool. This perl program is also capable to manipulate metadata from audio and video files.

Exiftool is also usable on Windows and Mac. This tool is very powerfull:

ExifTool supports many different metadata formats including EXIF, GPS, IPTC, XMP, JFIF, GeoTIFF, ICC Profile, Photoshop IRB, FlashPix, AFCP and ID3, Lyrics3, as well as the maker notes of many digital cameras by Canon, Casio, DJI, FLIR, FujiFilm, GE, GoPro, HP, JVC/Victor, Kodak, Leaf, Minolta/Konica-Minolta, Motorola, Nikon, Nintendo, Olympus/Epson, Panasonic/Leica, Pentax/Asahi, Phase One, Reconyx, Ricoh, Samsung, Sanyo, Sigma/Foveon and Sony.

To your third question: No. The metadata is included in the file itself. You need to do something with it, like importing and GIMP and exporting - GIMP may add an tag, that it was creates with GIMP. Of course there are formats, which have a separeted metadata file, but I am not talking about this. And dont forget the creation time thing and so on, but it is not hard to change some of it

To your fourth question: if you take photos, there may be information. It is possible to enable geotagging etc. The best option is to try it yourself. Take pictures with your Smartphone, make pictures with your computer or with something else and then read the metadata. Use exiftool for this task, but other programs are also ok. My smartphone only saves the brand and the model of my smartphone.

To your fifth question: delete metadata and take care, that there is nothing what can be traced to yourself (Names, Streets etc). Metadata is also available for PDF Files and many many more formats.