Tech is mainly for technology related strips, for example, computer jokes or how things work. A good example of a Tech series is knytrydr's Tony at Work, which features humor based on computer repair, and dealing with customers in that line of work.
Dresses and other composite images using various techniques and tricks have been put in the Tech section when really, this sort of thing belongs under the Experimental category. This type of confusion is the source of the 'computers and phones are tech you idiot' meme.