While sli.mg seems to be down, here's a list of working image hosting sites found in the v/vocatalog with big thank you to @dubbelnougat for keeping and maintaining the list.

/v/slimg - http://sli.mg & alt site http://ioimg.com ...sites down

/v/imgtc - https://imgtc.com/

/v/pixeldrain - http://pixeldra.in/

/v/imgur - http://imgur.com/

/v/voatpic - http://vopic.io/

http://imagus.co/ - I came across this one the other day

https://www.hpyshare.com/ - found at v/pics

http://ultraimg.com/ - found at v/pics

http://pomf.cat

http://cuntflaps.me

Feel free to add more in the comments and I'll update the post.