Why does one image not appear in an email?

[webmail-user]

In an email with 5 images only one of them is replaced by a box with a small icon of a page in the center instead of an image and I cannot figure out why this image is being blocked/not appearing. When I right-click on the image and select "Inspect Element" I get Adblock Plus references that say "Failed to load resource: the server responded with a status of 404 (Not Found)" and "Failed to load resource: the server responded with a status of 403 (Forbidden)". Is it possible that the image is no longer available from the sender of the email? Thanks for any help you may offer.   

[mfizzy]

Sound like the actual image was not in the email, but a link to the image was. When you tried to retrieve the image, the server it di not respond.