Musing.io has a great interface for adding you pictures to the post. Here is how you do it:
Step 1: Go to the image you want to add to your post and right click it.
Step 2: Select 'Copy Image Location'
Step 3: On top of the musing editor find the 'image url upload' sign and click it.
Step 4: Paste the image url and click 'ADD'
NOTE: For images on your computer - first upload them on websites like imgbb or imgur and then right click and copy image location to get the image url.