Dragging them could work, but it might malfunction randomly if you're using Firefox.
If you are using Steempress then WordPress has built in features to automatically resize your uploaded photos into quite a number of popular sizes and you just have to insert what you want into the post. But if you are using the default editor on Steemit you might want to look at this. I wrote it a long time ago, never thought that I would dig it out again :P
https://steemit.com/@lilacse/a-little-trick-to-make-photos-look-neat-in-posts
Gosh. How much weird stuff had I written in the past? Anyways, you have to view it on Steemit instead of Partiko if you are using that, the app's parser does funny things to part of the post. Have fun!
Posted using Partiko Android