I'd suggest tagging your posts for the Pictures category, then create and activate a Custom Menu, with a top level tab.

Next, add your tag pages to your Custom Menu and make those Tag pages as sub-menus under Pictures.

Don't forget to activate the custom menu, too.

Or, if you want to keep your current custom menu as your primary navigation, you can create another custom menu and add the Custom Menu widget to your sidebar.

I hope this helps! :)

The categorylist is like this, for example:

'Category'
Everyday
Outfits
Blog
Pictures"

and so on, but under it I will have something like this, for example:

'Pictures'
Nature
Animals
Buildings
Portrait
Photoshoot."

And put my posts into that, instead of have a bunch of picturecategorys under the categorylist. Or instead of have all the pictures under one name called 'pictures' or something.. Was a little difficult to explain, but I hope you get what I mean. If it is someone who understand and can explain better I would be thankful :) Is this possible in wordpress.com or only wordpress.org with plug-ins and html?