It will add slightly to the byte size of the graphic but since it is all one color it won't add much. A hit counter is a small script or program that increases a number every time a document is accessed from the server. If you believe that it will tell you how many times your documents have been accessed, you are mistaken. No counter can keep track of accesses from browser caches or proxy caches. Some counters even require access to a remote site, which may be down or overloaded, causing a delay in displaying your documents.
Most web servers log accesses to documents stored on the server machine.
There is no reason to display this number to your viewers, since they have no reference point to relate this number to. Not all service providers allow access to server logs, but many have scripts that will output information about accesses to a given user's documents. Consult your sysadmin or service provider for details. With server-side includes. Ask your webmaster if this is supported, and what the exact syntax is for your server.