use diagnostics; gives a little more info:

(F) You've said "use strict vars", which indicates that all variables must either be lexically scoped (using "my"), declared beforehand using "our", or explicitly qualified to say which package the global variable is in (using "::").

Also, you should use chomp instead of chop to strip off a trailing newline. So you need something like chomp(my $jpglist=<STDIN>);.