In my opinion the best way would be uploading it to Wikimedia Commons at https://commons.wikimedia.org/
They will have some annoying questions, but it is actually benefit - especially part about stating license and authorship. You can also upload to OSM Wiki - but it requires having account there with few edits and existing for few days.
If you are really unwilling to do either there are workarounds but it would be much cleaner for you to upload own photos.
(main annoyance is caused by copyright applying by default - and sadly “I’m ok with them being used freely” is not clear enough, you need to apply one of licenses to make them really reusable.
Options range from Template:CC-BY-SA-4.0-self - OpenStreetMap Wiki and Template:CC-BY-4.0-self - OpenStreetMap Wiki to Template:CC0-self - OpenStreetMap Wiki (just please do not use NC variants of CC licenses).