When you try to post your first welcome post on STEEM you notice there is no way to embed images directly to your post.
You always need to use an external site for your images. This may lead to be a problem in some cases. For example, popular image hosting Imgur blocks hotlinks to images. Other hostings suddenly remove images in case of user inactivity.
What we need here is an image hosting where you can upload unlimited images per post and will never have to worry about your images being removed for inactivity or hotlinks.
Here is a list of best of them proven to work with STEEM:
1) imgsafe.org - easy to use and it doesn't need an account. In addition to upload images from your local computer you may upload it directly from the web. Files are kept until you delete them.
2) ipfs.pics - it is IPFS based and will be compatible with upcoming IPFS support.
3) postimg.org works fine for steeming but site itself is slightly overloaded with an advertisement. In support of this service I can say that there is no registration or login, all you have to do is submit your picture.