I think you don't mean the title attribute, rather the filename - the src attribute.
If so -
Paths and filenames may be in any combination of upper and lower case letters. And scripts that address them on a local machine usually can as well, even different combinations, and still work. However, once on the server, if the actual case of the letters used in the path and filename do not agree with those in the script code, usually this will result in a broken image.
For example (on the server):
is not the same as (in the script code):
Servers and local machines vary, but this is almost always true of servers and local machines as noted.
To make it even more complicated, sometimes - depending upon what you're using to view the path and filename, it will appear to be all lower case even when it isn't. This can be true in Windows 7's Windows Explorer (the file manager thing, not the browser), and probably in many other cases. Looking at these things in a DOS window (from the command prompt) should show the true state of affairs. But, as this is so critical, any decent ftp program should also show the actual filename rather than the lower case version. But since the viewing of files in a program is often handled by the OS, this may not always be true.
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