This sounds more like an issue with phpMyAdmin itself (not MySQL or PHP in general), so you'd probably be better off looking for support in phpMyAdmin's Support section.
Out of curiosity, though, is there any particular reason why you're wanting to store the actual image data in the DB in the first place? More often than not, this is a bad idea as compared to simply storing the files in the file system and instead only storing metadata about those files in the DB.