According to this meta post questions in the general form of how do I do X are frowned upon because they tend to be brainstorming questions without a solid or clear answer.
Conversely, this meta post states the questions asking for tutorials about achieving a certain effect get useful answers (about the effect, not the tutorial):
I think that they get reasonable answers, with suggestions on how to achieve the effect, rather than pointers to tutorials
This makes me think that a clear question about a clear effect should be on topic even though it is essentially a "How-To" question. What is less clear is if I can ask for help on how to achieve an effect with a certain program.
The reason I ask is because I am starting a blog, and my graphic design skills are quite poor. I recognize that blogs with images are more interesting than those without images. I don't have the extra cash to actually hire a designer or pay for a graphics design software license. This means I need to use a free tool like Gimp and generate my own images. I would like to ask for help here if the question is on-topic and not considered too localized.
For context my current question would be:
How can I achieve the effect in the picture below when starting from a screenshot, using Gimp or another free software package. I would also like to know what the effect is called if it has a name.