Many thanks tgtje.
My php version is 5.6.15.
GD is enabled - bundled (2.1.0 compatible), enabled for all image formats.
No files have been changed since 2015, except those in the cache folder.
I know, one day I will have to update to V2 to avoid problems in the future.
I just modified too many template and core files and that's why I've been delaying the upgrading process.
Guys, how can I log in to my admin panel if can't see the code?
Maybe I can somehow turn the image code verification off in the database?