Welcome to the fragile world of MyISAM tables.
You can always drop the table then create it again using the database schema vbulletin uses.

Code:
DROP TABLE IF EXISTS `picture`;
CREATE TABLE IF NOT EXISTS `picture` (
  `pictureid` int(10) unsigned NOT NULL auto_increment,
  `userid` int(10) unsigned NOT NULL default '0',
  `caption` text,
  `extension` varchar(20) character set latin1 collate latin1_bin NOT NULL default '',
  `filedata` mediumblob,
  `filesize` int(10) unsigned NOT NULL default '0',
  `width` smallint(5) unsigned NOT NULL default '0',
  `height` smallint(5) unsigned NOT NULL default '0',
  `thumbnail` mediumblob,
  `thumbnail_filesize` int(10) unsigned NOT NULL default '0',
  `thumbnail_width` smallint(5) unsigned NOT NULL default '0',
  `thumbnail_height` smallint(5) unsigned NOT NULL default '0',
  `thumbnail_dateline` int(10) unsigned NOT NULL default '0',
  `idhash` varchar(32) NOT NULL default '',
  `reportthreadid` int(10) unsigned NOT NULL default '0',
  `state` enum('visible','moderation') NOT NULL default 'visible',
  PRIMARY KEY  (`pictureid`),
  KEY `userid` (`userid`)
) ENGINE=MyISAM;
Note: This is a vBulletin 3.7.2 PL1 schema, as far as I know.
Hope this helps.

EDIT: Assuming you recreate this picture table from scratch, you should also truncate (empty) the following tables as well: albumpicture, picturecomment, picturecomment_hash