New answers tagged copyright
In addition to Pit's answer, also there's matter of copyrighted material. Most of the companies have registered name / trademark, so you need to ask them if they are willing to participate.
Depends on the company. Some might be ok with you using the logo, some might not be ok, some might even require you do follow certain rules. For example Microsoft has very specific rules for using their logo: https://www.microsoft.com/en-us/legal/intellectualproperty/trademarks/usage/logo.aspx
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