I can't preview JPG image in browser

My English is not good,So please keep patient.
Thx, XD.

Steps to reproduce
Just installed the owncloud..

Expected behaviour
The thumbnail should show in the browser and I can preview the pic

Actual behaviour
I just can see the default pic,Black and white.
And owncloud told me " Could not generate a preview of this file.".
And the console print "500Error".

Server configuration
Operating system:CentOS 7
Web server:Nginx 1.10.3
Database:Mysql
PHP version:7.0.17
ownCloud version (see ownCloud admin page):9.1.4
Updated from an older ownCloud or fresh install:New
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption):Used the Nginx. Not more.

ownCloud log (data/owncloud.log)
no log...Not to print it.

Nginx.conf

user  www;
worker_processes  4;
#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;
#pid        logs/nginx.pid;
events {
    worker_connections  1024;
}
http {
    include       mime.types;
    default_type  application/octet-stream;
    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
#                  '$status $body_bytes_sent "$http_referer" '
#                  '"$http_user_agent" "$http_x_forwarded_for"';

#access_log  logs/access.log  main;

sendfile        on;
#tcp_nopush     on;

keepalive_timeout  60;

#gzip  on;

upstream php-handler {
    server 127.0.0.1:9000;
    #server unix:/var/run/php5-fpm.sock;
}

server{
    listen       80;
    server_name  localhost i.hurryhuang.cn hurryhuang.cn www.hurryhuang.cn;
    rewrite ^/(.*)$ http://hurryhuang.cn:88/$1 permanent;
}

server {
    listen       88;
    server_name  localhost i.hurryhuang.cn hurryhuang.cn www.hurryhuang.cn;
    root	     /home/www/hurry;

    charset UTF-8;

    #access_log  logs/host.access.log  main;

    location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
    }

    location / {
        index  index.html index.htm;
    }

    location = /.well-known/carddav {
        return 301 $scheme://$host/owncloud/remote.php/dav;
    }

    location /.well-known/acme-challenge { }

    location ^~ /owncloud {
        #keepalive_timeout 6600;
        fastcgi_read_timeout 1200;
        fastcgi_request_buffering off;
        client_max_body_size 30G;
        client_body_temp_path /tmp;
        fastcgi_buffers 64 4K;
        gzip off;

        error_page 403 /owncloud/core/templates/403.php;
        error_page 404 /owncloud/core/templates/404.php;

        location /owncloud {
            rewrite ^ /owncloud/index.php$uri;
        }

        location ~ ^/owncloud/(?:build|tests|config|lib|3rdparty|templates|data)/ {
            return 404;
        }
        location ~ ^/owncloud/(?:\.|autotest|occ|issue|indie|db_|console) {
            return 404;
        }

        location ~ ^/owncloud/(?:index|remote|public|cron|core/ajax/update|status|ocs/v[12]|updater/.+|ocs-provider/.+|core/templates/40[34])\.php(?:$|/) {
            fastcgi_split_path_info ^(.+\.php)(/.*)$;
            include fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_param PATH_INFO $fastcgi_path_info;
            #fastcgi_param HTTPS on;
            #fastcgi_param modHeadersAvailable true; #Avoid sending the security headers twice
            fastcgi_param front_controller_active true;
            fastcgi_pass php-handler;
            fastcgi_intercept_errors on;
            fastcgi_request_buffering off; #Available since nginx 1.7.11
        }

        location ~ ^/owncloud/(?:updater|ocs-provider)(?:$|/) {
            try_files $uri $uri/ =404;
            index index.php;
        }

        # Adding the cache control header for js and css files
        # Make sure it is BELOW the PHP block
        location ~* \.(?:css|js)$ {
            try_files $uri /owncloud/index.php$uri$is_args$args;
            add_header Cache-Control "public, max-age=7200";
            # Optional: Don't log access to assets
            access_log off;
        }

        location ~* \.(?:svg|gif|png|html|ttf|woff|ico|jpg|jpeg)$ {
            try_files $uri /owncloud/index.php$uri$is_args$args;
            # Optional: Don't log access to other assets
            access_log off;
        }
    }

    location ~ ^/(?:\.htaccess|data|config|db_structure\.xml|README){ 
		deny all; 
    } 

    error_page  404              /404.html;


    error_page   500 502 503 504  /50x.html;
    
    location ~ \.php(?:$|/) {
    fastcgi_param PATH_INFO $fastcgi_path_info; 
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;
  	    include        fastcgi_params;
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    
    location ~ /\.ht {
        deny  all;
    }
}
}

www.conf

pm.process_idle_timeout = 60s;
env[HOSTNAME] = $HOSTNAME
env[PATH] = /usr/local/bin:/usr/bin:/bin
env[TMP] = /tmp
env[TMPDIR] = /tmp
env[TEMP] = /tmp
php_flag[display_errors] = off
php_admin_value[error_log] = /var/log/fpm-php.www.log
php_admin_flag[log_errors] = on
php_admin_value[memory_limit] = 256M

The owncloud config.php

  'logtimezone' => 'Asia/Shanghai',
  'installed' => true,
  'mail_smtpmode' => 'smtp',
  'logdateformat' => 'Y-F-d H:i:s',
  'enable_previews' => true,
  'preview_max_x' => 3048,
  'preview_max_y' => 3048,
  'preview_max_scale_factor' => 10,
  'preview_max_filesize_image' => 60,

A 500 error means "internal server errors" [1] and those are definitely logged somewhere in your logfiles. To be able to help here the matching error from your logfile needs to be provided.

[1]

I will to do this to looking for error.But I'm sure the log of owncloud not to record this error,I maybe can check other‘s log to fix this.

Normally, it must be in your webserver logfiles.