Dear,
I tried to upload the photos in K2 item from frontend but after upload image is not displayed and is not upload, the same happens with attachment From backend all work perfectly. This is the first time I use frontend.
Do I need something to set?

Joomla ver: 3.3.3.
K2 ver: 2.6.8.

Any help is welcome. Thank you.

Hello Sandro,

This post will help you:
getk2.org/documentation/tips-a-tricks/201-allowing-users-to-submit-content

You will also find extra settings in K2's parameters.

Thank you very much for your help, this article have been already found, and through him, I've set the parameters. All described in it work. Problem is when I upload picture or attachment through corresponding tab, the system works, but nothing happens after complete the task.
Attachments can not even upload a photo too. For photo album I use Simple Image Gallery Pro, and I have the same problem, File was not uploaded.

Then the problem is not with K2 nor SigPro.
Are you using security extensions or custom .htaccess protection?

I'll try a few more things, but all it works very good in the backend side.

Security plugins in general do not block any actions from the backend. That is why you are not having issues.