Blue_question_mark_icon.svg is from WikiMedia Commons by "User:Isarra"
and is "based on the linux biolinum font" and as is listed in the public domain:
http://commons.wikimedia.org/wiki/File:Blue_question_mark_icon.svg

For reference, the biolinium font is licensed under "SIL Open Font License v1.10".
http://www.fontsquirrel.com/fonts/linux-biolinum

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Info_blauw.png is from Wikimedia Commons by "Wolf Lambert" and was placed into the public domain.
http://commons.wikimedia.org/wiki/File:Info_blauw.png

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Information_icon4.svg is from Wikimedia Commons by "penubag" and was placed into the public domain
http://commons.wikimedia.org/wiki/File:Information_icon4.svg