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if you do not use the source, it means you consider that the work is your own. and if the work is proven to belong to someone else, then you are considered plagiarism.
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BS.

If you use an image from certain sites like Pixabay, they specifically give you permission to use their images without - her is a sample of what they say:

• All images are free - even for commercial use! No attributions required.

If you give false info, then even when you speak the truth, you will be ignored. Make certain you have your facts as they are in real life, not as you 'think' they are.