Let’s visit the website and see how it is and what it says.
this is enough to give the hint that this is classic MD5 collision problem.
for this challenge we will use fastcoll
To it hassle free i downloaded the pre-made hash collision MD5 hash file
wget https://www.mathstat.dal.ca/~selinger/md5collision/hello
wget https://www.mathstat.dal.ca/~selinger/md5collision/erase
md5sum hello erase
mv hello a.jpg
mv erase b.jpg
now upload both one by one.
here you can see the match is completed and now you can scroll down and capture the flag.