While this is frustrating, there are ways around it.
Don’t take a picture of your firearm
Take a picture of the side of the firearm that doesn’t have the serial number
Cover the serial number on your firearm for pictures you’ll post on social media
I do have pictures of my firearms with their serial numbers clearly shown - but they’re not posted on social media. They’re in a file with all of my insurance information.
What other reasons do you have photos of your firearms? Where do you keep those photos?
Doesn’t matter. It’s too late for this. Once you save it there, it stays there forever.
You actually won’t delete the file, just pointer to this file, so it can be retrieved in future (not for you of course)
With most cell phones backing up pictures to the cloud it wouldn’t be a big step for Google to scan photos you didn’t post as well. This will put a damper on the collector community, photos and serial numbers are a big part of those discussions.
I have photos of the serial numbers saved within my “notes” on my phone just in case any are ever stolen. That is the only reason I have them stored on my phone. I am very cautious about posting them online in general just due to way social media is and the knee jerk reactions employers or potential employers have.
I would suggest printing them out in case of the accidental destruction of your phone. I’ve heard of phones being flushed, dropped in port-a-potties, flying off the roof of the car, dropped on the floor… the list goes on. Having a hard copy of the photos stored somewhere can be incredibly helpful.
I have photos of my firearms (side w/o serial numbers) in a document and then in a separate document I have a list of serial numbers for all of the important things covered by my insurance with a simple code indicator of what each item really is.
accidents are happening alot this year. I fear El Nino has really changed the climate and made 
I’m not shooting at my phone. 
