My advice is to use imgur, imgbb is suck since there's few moment the images is error and it will show "Bitcointalk.org image proxy: Invalid image" even though the images is appeared before and yo're using the correct BBCode. Don't forget there's a limitation to upload an image, the maximum is only 2MB, if you upload higher than 2MB the images will error too.
You are correct @Solosanz, imgbb is not reliable. At first, the pictures would be valid and okay but after a few hours or days, the images would show that they image is invalid. And the most challenging part of the situation is that there is no known reason for this. At first, I thought that it was because I didn't register but it persisted after registration.
I have not tried imgur but after observing some images in the forum, I concluded that that website is the best. I have to devise a means to register because their services is not offered at my location.