Exact error message:
esppic:24:8: error: conflicting declaration 'String filename'
24 | String filename;
| ^~~~~~~~
In file included from /home/hari/.arduino15/packages/esp8266/hardware/esp8266/3.0.2/libraries/ESP8266WebServer/src/ESP8266WebServer.h:341,
from /home/hari/Downloads/esppic.sqfs_FILES/esppic/esppic.ino:10:
/home/hari/.arduino15/packages/esp8266/hardware/esp8266/3.0.2/libraries/ESP8266WebServer/src/Parsing-impl.h:33:19: note: previous declaration as 'const char filename [9]'
33 | static const char filename[] PROGMEM = "filename";
It is possible that, this variable got introduced after the release of ESPPIC tool. Anyway, this source can not be compiled without renaming this variable