Not citing the source of photos is plagiarism. Here is a post on why this is bad, and here is how easy it is to find allowed photos.

Not indicating that the content you copy/paste is not your original works could be seen as plagiarism.

Please refrain from using #photography for posting art, posting graphics, posting other users photos without commentary, etc. Abusing tags can potentially lead to people flagging you, even from dan himself.

#steemitphotochallenge is used by a specific type of content. You can find information here for the Steemit Photo Challenge

Thank You! ☙