Each member is allowed 19.5 MB of space to drag or place files/images in their post. You can see this at the bottom of you post after hitting reply.
Some members have noticed that they are near, or out of space. It is up to each member to manage their own space. Every member is able to create space by going to your name in the upper right and selecting "My Attachments." There is a garbage can icon on the righthand side of each attachment. A member is able to delete an attachment that is no longer relevant, to create more space. When you do so, anywhere the attachment was used will then contain a broken image or link. Pay attention to the size, the bigger attachment you delete, (obviously) the more room you will create. Good luck.