No, it's not. Sometimes people remove unnecessary graphical elements to make things fit on a display, or modify them with something they find more appealing.
Anyways, it is not illegal to take FreeNAS and do almost anything with it. It's distributed under the BSD license. Kirk famously summarized this:
"you had copyright, which is what the big companies use to lock everything up; you had copyleft, which is free software's way of making sure they can't lock it up; and then Berkeley had what we called ‘copycenter’, which is ‘take it down to the copy center and make as many copies as you want.'"
The license reads:
Code:
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
The license doesn't preclude you from removing logos. It only really prevents you from removing the existing copyright notices and related materials.
With that said, I'm going to note that iXsystems has trademarked "FreeNAS", which means that if someone did want to go and release a variation of some sort, it would be dangerous and hazardous to call it FreeNAS, or to include the iXsystems logo, which might imply that the variant was sanctioned in some form.
In other words, someone who is aware of the legalities of the situation, and maybe wants to roll their own distribution, maybe to make their own NAS product, it's not illegal for them to do so, but it is legally dangerous for them to call it FreeNAS, or to use the iXsystems logo.
With that having been said, I'm going to note that anyone who has to ASK about how to do this is unlikely to be doing anything major. I mean, really, web browser, hover, "View Image Info", well, look, there they are, the file names are "freenas-logo.png" and "ix_logo.png", now how hard was that.