You want requested URLs to be valid whether uppercase or lowercase letters are used.
Use mod_speling to make URLs case-insensitive:
The mod_speling module is part of the standard Apache distribution but is not enabled by default, so you need to explicitly enable it.
In addition to making URLs case-insensitive, mod_speling, as the name implies, provides simple spellchecking capability. In particular, in the case of a "not found" error, mod_speling attempts to find files that may have been intended, based on similar spelling, transposed letters, or perhaps letters swapped with similar-looking numbers, like O for o and i for 1.
When mod_speling is installed, it may be turned on for a particular scope (such as a directory, virtual host, or the entire server) by setting the CheckSpelling directive to On.
And, yes, that is the correct spelling of the module name.