Hey Tekoa,
I am sorry for the delay of this reply,
May i know what editor you using now? Because when you insert image into blog content through Tiny-mce or Jce Editor, they will allow you to add the alt tag in the image. You can refer on my attached screenshot below.
By the way, If you using Easyblog build-in composer, currently we do not have a option to add alt into image yet.