If you are uploading it using any FTP client then try to upload it through cpanel -> File Manager as sometimes images not upload properly through FTP client. DON.
Depends on how you are uploading the pictures, if you are using the uploader built into wordpress, check the permissions on the folder it is uploading to, and make sure there isn't a limit on the size of a file that you can upload, or that the picture is too big to upload that way. At last resort, you could always try a different method, like a free image hosting site such as http://share.wiredtron.com
If you are on a PC first clear your cache and reload the page. Then right click on the X and take note of the path. Then go to your Cpanel or use an FTP program to see if the image is in the folder the path is pointing to. Sometimes when you change themes they paths are not recognized for whatever reason.
I think You have inserted Image URL to Added an Image & now image is Removed from the source that's why this happen Check this again or you can Delete this image if you have uploaded instead adding direct URL.. & then Re-uplod it to post then See whats happen
Hey try clicking on settings and then going on Misc. Make sure the wordpress upload directory is correct. I had this issue aswell and this fixed my problem.
How are you uploading your images? Via FTP or using Wordpress insert function in the write panel? Also, a link to your site would be nice so we can see what's going on there.