It is HIGHLY important to source art. It is HOURS of sketching, inking/lining, and coloring the piece. The least you could do to the artist is mention them when you use their drawings...
Artists are already a degraded and often underpaid (or even NEVER PAID) for their stuff so yes, sourcing, mentioning and crediting their work when you post it somewhere else is already the best you could do if you don't buy their art or anything...

Just my two cents! Have a nice day.
Good post raising awareness for everyone about artists' struggles.