This may indicate a permissions problem with your WordPress uploads directory.
Firstly please make sure that you have the right permissions on /uploads folder.
$ sudo chmod -R 755 uploads/
Then if still nothing happens, please check the owner permissions.
$ ls -l
total 24
-rw-r--r-- 1 root root 28 Jan 26 13:44 index.php
drwxr-xr-x 16 root root 4096 Jan 26 14:50 plugins
drwxr-xr-x 7 root root 4096 Jan 26 13:44 themes
drwxr-xr-x 2 root root 4096 Jan 26 13:44 upgrade
drwxr-xr-x 11 root root 4096 Jan 26 13:44 uploads
Let’s offer the right permissions. As we can see the uploads folder has the root owner. The owner of Nginx/Apache servers is www-data
$ sudo chown -R www-data:www-data ./uploads/
Now if you check again, the owner is changed and the permissions 755 are set.
$ ls -l
total 24
-rw-r--r-- 1 root root 28 Jan 26 13:44 index.php
drwxr-xr-x 16 root root 4096 Jan 26 14:50 plugins
drwxr-xr-x 7 root root 4096 Jan 26 13:44 themes
drwxr-xr-x 2 root root 4096 Jan 26 13:44 upgrade
drwxr-xr-x 11 www-data www-data 4096 Jan 26 13:44 uploads
That’s it!
