Can a user sell my software (MIT license) without modification? Basically, I was just wondering if I release a piece of open source software under the MIT license, does that mean that someone could take it and sell it onto people without doing any modification to it?
Yes. The license itself is really just one sentence long, and states explicitly that this is allowed. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
This is unlikely to be a problem. There are many companies that have already registered software-related trademarks prominently involving an X or the name Xcom. That Twitter has changed to X branding does not substantially change this general situation. With trademarks, the general question is whether similar branding causes confusion. It is unlikely that someone would confuse the X display server / X.Org project / X.Org Foundation with the social media service now being branded as X or x.com. Of course, anyone can sue anyone, the real question is whether that's possible successfully. Here, I have my doubts that x.com could successfully demonstrate confusion in its favour. It is worth noting that the X.Org Foundation does not seem to hold any relevant trademark registrations at all. This is not unusual for Open Source software projects and doesn't mean that X.Org has no rights, but does make a defense a bit more difficult. However, there also doesn't seem to be a relevant registration by the ex-Twitter company or by the X Corp. The x.org domain name is unlikely to be threatened. If the x.org domain name was being used in bad faith it could maybe be seized, but the X.Org Foundation has a pretty strong claim on this name. For historical context, both x.com and x.org were among the six single-letter .org/.net/.com domain names when such registrations were stopped in 1993. But while x.com has been pretty much dormant since that company was renamed to PayPal, x.org has (I think) always been associated with the display server software, and has been used continuously by the X.Org Foundation since its establishment in 2004.
It is illegal to make copies of copyrighted materials without license. In the case of software, obviously it will be illegal to make copies by copying and installing the software without a license, but we are not talking about that. If I have a legitimate license of say Photoshop, and I start the application, parts or all of the code will be loaded into the RAM of my computer, which is a copy. According to copyright law, it is legal for me to make that copy. You are allowed to copy legitimately owned software into RAM to execute it. If your copy of Photoshop is illegal, and you start the application, the copy that is made into RAM is again copyright infringement. Having read the software license for the software that you get when you buy a Mac, it seems that if you steal my computer and just start the operating system, you are committing copyright infringement, and it seems that if you buy such a stolen computer and just start the operating system, you are committing copyright infringement as well, because the license that I received when I purchased the computer covers anyone using it with my permission, and covers anyone who legally buys the computer from me, but doesn't cover a thief. Now does this affect the work that you did? No, you have the full copyright on your work. Copyright law doesn't require that your tools are all used legitimately.
You seem to assume that copyrights require paperwork such as registration. This is wrong, copyright is automatic. And it prevents the downloader from making the sort of change that you suggest. In fact, it prevents the downloader from using your template at all. The only reason the downloader can use that template is because you've granted him a specific license to ignore some copyright rules, but the default remains. And you did not grant the right to alter the template to free users.
Generally, it's illegal. You are creating a derivative work and you are not allowed to do that without the permission of the copyright holder. Some jurisdictions may have exceptions, such as fair use under US law. However, this generally protects uses that are intended to comment on or parody the work. It doesn't sound like that is the purpose of your image modification. NOT including: faceswaps, modifications that would shame or affect negatively the reputation of the actors on the image. That doesn't make it legal. I share it in a way that I don't make any economic profit out of it, and clearly stating that it is a modified image (not sure if inside the image, or in the caption under it) and state who is the legal owner of the original image. That doesn't make it legal, either.
If you develop a program yourself and it wasn't a work made for hire, then the program is yours to do with as you please. You hold the copyright to it. Many developers choose existing licencing arrangements or they can choose to create a license on their own, or using an attorney. And sometimes they choose to release their programs into the public domain. If you release it into the public domain, you are essentially giving up your copyright. The IDE (Integrated Development Environment) you used to develop your program does not dictate what licenses you can use. There are some existing licenses that others use (which you are free to use or NOT to use) give varying protections to you regarding what you are allowing others to do; right of others to copy, right of others to modify, right of others to distribute, rights to sub-licence, and so on. One of the licensing schemes is the GNU General Public License (GPL). But there are many others, too many to list here.
Unless you have a legally valid IP right related to the specification that statement is meaningless. When a software license is granted it is based on the copyright of the code. The copyright of the spec. just stops people from copying the spec - it does not protect the information in it. You can restrict copying of the spec. under copyright, you can make up a name for the spec (like USB or Bluetooth) and get a trademark and only allow the trademark use in limited cases(doesn’t stop implementation of the spec), or get a patent that would be necessarily infringed if something complying with the spec was created and used, sold, made, etc. or you can keep it secret and only show it to people who contractually agreed with your terms.
While I agree that the license required for your use case isn't particularly obvious to me, the page you have linked to includes the following paragraph: Need help picking your license? Just shoot us an email at themes@getbootstrap.com and we’ll help you decide which license makes sense for your needs! So in this case, my recommendation would be to get in touch as described, that way you will know for sure that you are properly licensed.