Can you access uploads after reinstalling your OS, if you don't register an email address?
Unfortunately, if you reinstalled your OS without registering an email your previous captures will no longer be accessible. To avoid this we place messages reminding you to create an account in multiple places in Gyazo.
Why is this?
Gyazo uses an Auto Login system by default, which allows you to start an account quickly without needing an email.
If you reinstall your operating system, the unique key created by Auto Login is no longer saved, so your device is no longer linked with your data in our system.
Any Gyazo capture links you shared publicly will remain publicly accessible and any unshared links will remain private.
Upgrading to Gyazo Pro will not link an unlinked account. Do not upgrade hoping to regain access to previous uploads. However, if you use an email you can see uploads from before upgrading. See Can you see captures from before subscribing to Gyazo Pro? for more details.
If you have uploaded from another device which has the same operating system, you may be able to access those captures.