Saw your message in the chat. Thought I'll reply here.
A few meme challenge I saw requires use of a image that is provided and tag with a requested tag so the judge can find it . So, you should find the particular challenge announcement and read the rules.
One I have tried before is #memechallenge and you can find the post like that.
https://steemit.com/created/memechallenge
Scrolling down long enough you should find the annoucement post.
May be a good idea to FOLLOW the organiser so you get the post in your feed in future.