We have recently had several reports of the Upload/Embed Image Tool being slow or unresponsive. If you click the button to upload an image and the circle spins indefinitely then you are experiencing this too.
We have experienced the slow performance ourselves as well. As far as we can tell, t
One tip if this is happening and you are pressed for time is to choose the "Download" button and save the image to your computer and use the built-in Canvas upload tool. As noted above, Canvas gives preferential treatment to its own tools so they shouldn't experience the lag that can come through using the API.
Finally, we are wrapping up a new version of the Upload/Embed Image tool and one of the improvements is a little more transparency in this process. The new version will let you know when the tool is waiting on Canvas. It will also only check 12 times. If the count reaches 12, Design Tools will return a message about high activity and provide a link that can be clicked at a later time if you want to wait for Canvas to process the image. This will prevent the tool from expounding the server congestion.