I'm getting that error every time I try to upload an image to a thread. It's a picture from my phone camera that I'm normally able to upload.
Try taking a screenshot and uploading that as a test, or try converting the image to a JPEG if it isn't already. I have seen that as well and I think it was due to the format on my iPhone (HEIC)
What kind of phone is it? Some phones, especially iphone, will now default to HEIC format, instead of JPG or JPEG. Most other programs cant deal with those photos. Check the fie extension. If that's the problem,there are free converters available.
I'm using Real HEIC to JPEG Converter, but there lots of others .
I realized that I can't send photos through the phone, whether on phone or desktop mode. If you have access to a PC maybe throw it up on there, or put it on your google drive/iphone drive, and share a link?