Since Monday 18 February 2019 an error has occurred in the process for uploading images using Pasteboard, which has been the recommended service since this site was launched. The result is that images uploaded using the CDN link provided by Pasteboard cannot be displayed at present. See http://physics.qandaexchange.com/?qa=3386/pasteboard-images-not-displayed.
It is not known if or when this problem will be fixed. Consequently, it is highly recommended to use IMGUR rather than Pasteboard for all future posts.
INSTRUCTIONS FOR USING IMGUR (https://imgur.com/upload)
Use CTRL-V or BROWSE or DRAG-AND-DROP to paste your image. Enter a title (optional).
Do not use the link given at this stage. Instead click on the drop-down menu to the right of
the Copy button. Select "Get Share Links", then select "BBCode (Forums)." Click on the "Copy" button to the right to copy this URL.
Do not delete the image in Imgur after you have pasted the URL into PhysicsQandA.
Return to Physics QandA website. Click on the image icon at the top of the Question or Answer editing box, delete the text already there and paste from the clipboard. Delete the prefix [img}.
INSTRUCTIONS FOR USING PASTEBOARD (https://pasteboard.co/)
Use CTRL-V or SELECT IMAGE or DRAG-AND-DROP to paste your image, then click UPLOAD.
Do not use the link given at this stage ("Here's your link"). Instead click on GO TO IMAGE and copy the Embed URL link at the top right (https://cdn.pbrd.co/images/....).
Click on the image icon at the top of the Question or Answer editing box and paste the "Embed URL" link.
Do not delete the image in Pasteboard after you have pasted the URL into PhysicsQandA.