Are these on- or off-topic?
If off-topic, should these be moved to theoretical CS?
I think the question about computational complexity isn't a good fit for the site, if only because computational complexity of algorithms tends to be more of a theoretical CS question (exceptions for SciComp would probably be along the lines of graph-theoretic algorithms or numerical linear algebra).
The question about optimization algorithms could be on-topic, but that poster's question leaves much to be desired. It's not clear what type of problem he is trying to set up.
I could see image processing questions being on topic if they involve numerical algorithms. Otherwise, I think they're probably a better fit elsewhere.