Posting other people’s images without credit when you know who created it is not cool.
Reblogging the work of artists/photographers/writers and actively removing their credit is even worse.
The set-up of Tumblr encourages this somewhat - it’s easy to instantaneously reblog without giving much thought to where an image came from. And it seems to have led to the rise of a culture of people who just reblog things they think are cool as if to say “look how good my taste is”. Which, you know, that’s up to you, that’s fine, but consider this; each image you’re reblogging was created with love and time and hard work. The person who made it deserves to have their hand in its creation acknowledged and respected. If they’ve added some text along with the image, chances are because that is part of how they want to present the work.
I really wish Tumblr’s reblog feature wouldn’t allow the reblogger to remove any of the content, only add to it, but it doesn’t. So it’s up to you. Don’t be a jerk. Keep the credit in, keep the text in. Show a little respect to the people who create the things you like.
EDIT: A couple of people seem confused by me saying “keep the text in”. I’m referring to the text the creator has included, not the commentary added by people as it’s reblogged.