Maybe an extension or plugin issues...
From your Safari menu bar click Safari > Preferences then select the Extensions tab. If you have any installed, turn that OFF, quit then relaunch Safari to test.
If it's not an extensions issue, back to the menu bar click Safari > Preferences > Security.
Deselect: Enable plug ins. Quit then relaunch Safari to test.
If that helped, then you have one or more Safari add ons causing this.
Follow the instructions for troubleshooting plugins here > Safari: Unsupported third-party add-ons may cause Safari to unexpectedly quit or have performance issues
If it's not a plugin issue, go to ~/Library/Preferences. Move the com.apple.Safari.plist file from the Preferences folder to the Desktop.
Quit then relaunch Safari to test. If that helped, move the .pilst file to the Trash. If not, move it back to the Preferences folder.
edited by: cs
The image displayed in Safari cover flow looks like it corresponds to what was displayed in the browser when the snapshot was captured. I was able to get a better cover flow image by deleting the bookmark and clearing the cache, then lengthening the browser window and re-visiting the page.