When it comes to describing things that are only recognized visually, "by sight" is a phrase that is commonly used. However, there are many other synonyms that can be used to convey the same meaning. Some examples include "visually", "through the eyes", or "based on appearance". "By appearance" is another term that can be used to describe something that is recognized solely by the way it looks. "By observation" is yet another alternative that can be used when referring to something that is seen with one's eyes. Ultimately, selecting the right synonym will depend on the context in which the phrase is being used and the desired tone or style of the writing.