[c++] cannot convert 'std::basic_string<char>' to 'const char*' for argument '1' to 'int system(const char*)'

The addition of a string literal with an std::string yields another std::string. system expects a const char*. You can use std::string::c_str() for that:

string name = "john";
string tmp = " quickscan.exe resolution 300 selectscanner jpg showui showprogress filename '"+name+".jpg'"
system(tmp.c_str());