I have experienced the above (missing thumbnail option) for a non-plugin WP-installation based on Scientific Linux 45. GD was not missing, but php-gd was and WordPress did NOT complain about missing gd.
Using the hints here and my own findings I updated gd and installed php-gd. Still no thumbnail option.
However, a newly installed WordPress weblog2 did have this thumbnail option.
Work-around:
1. Export all your Worpress stuff, using “Manage->export”.
(Save it on your browser-computer, make sure it is readable!)
1.a. Create a new weblog.
OR:
2. Login to your server.
3. Rename wp-config.php.
4. Backup your pictures.
DO NOT REMOVE the picture-files in “upload/…”
5. Drop the database tables from your WordPress weblog
(Maybe there is an easier way?)
6. Make sure /etc/php.ini allows enough memory to
php-scripts.
48M works for me. 8MB was far too little!
7. Run a new install.
8. Go to write->upload and try to upload an image.
Enjoy “Thumbnails option”
9. Import your XML file from the browser computer
using manage->import
The old pictures will NOT be showed anymore
so you may prefer to upload them again.
I am sorry that I do not have a better work-around.
There must be a way to fool WordPress to re-run the
installation-initialization of the options in the
database.