besides
imgur.com which is currently having problems and
imgbb.com as you mentioned.
postimg.cc is also a good alternative in my opinion, because I have been using it for a long time and until now I have never had any problems with the image display.
In fact, I have an account and save a lot of pictures that I've uploaded before.
I agree with
taufik123.
In my formatting of scam reports, I mainly use
https://postimages.org/ as my main source of posting images in the forum. I tried using imgur but most of the time, I experienced the same error. For some reason, the images in imgur expires and it appears as an "invalid image" after a given set of time.
You can check my history of topics that I created and almost every picture that I posted, I used postimage. I hope you settle and consider this solution, OP.