FAQ - Legality & Ettiquette
Sources of that may answer questions or contribute to discussion in a more long-form way are as follows:
Are you or this project affiliated with Wizards of the Coast?
No, this is an unofficial fan project.
Are these real Magic: the Gathering cards that can be used in all settings a Magic: the Gathering card could be used?
No. These are not real magic cards, and there are many circumstances where using these would be against Wizards policy, Magic tournaments rules, or social agreements.
Is this legal/against Wizards policy on fan content?
At the time this project was originally published, Wizards of the Coast had a proxy policy outlined here. Additionally, myself and any other contributors to this project take zero credit for any of the assets or graphic design elements used in existing magic cards.
This project has been conducted under the assumption that distributing such a tool is legal and within Wizard's fan content & proxy policies, that printing out these proxies is functionally equivalent to printing out a scan of a card, but with the intent to make clear that these are proxies & to minimise resource use.
From the proxy policy article:
Wizards of the Coast has no desire to police playtest cards made for personal, non-commercial use [...]
Can I use these in a sanctioned tournament?
No, that is against Wizards of the Coast policy wrt sanctioned tournaments. In the proxy policy article it is made clear that only authentic magic cards are legal in sanctioned play:
Cards used in DCI-sanctioned events must be authentic Magic cards.
Note that sanctioned tournaments include (but are not limited to) Commander fests, pre-releases, and FNM events, meaning that these proxies cannot be used at these events unless issued as an emergency tool, but a judge is far more likely to prefer writing the card name of the card being proxied on a basic land due to not requiring the tools to print & cut out a proxy.
Can I use these casually at my LGS?
Ask your LGS what their policy is on proxies before turning up with proxies for casual play. LGSs make money off selling sealed product and singles to their customers, and using proxies even casually without permission may cause tension between you and your LGS.
Can I print & sell these to other people?
No, that is against Wizard's fan content policy and Proxy policy. This is fan content, neither you nor I can require payment for its use. In the fan policy article:
You can’t require payments, surveys, downloads, subscriptions, or email registration to access your Fan Content;
In terms of the proxy policy:
Wizards of the Coast has no desire to police playtest cards made for personal, non-commercial use [...]
Wizards of the Coast owns the assets used in the production of these proxies. Doing so is in violation of intellectual property & not respectful to the policies referenced in this article. This is a free project that aims to make playtesting decks with proxies take as few resources as possible while not causing dissonance between graphic design of proxies & that of real magic cards.