New guy question

Hi guys/girls,
What size and format do photos have to be to post on this forum ??
Have re-sized and dropped quality to try and post them but 
" Computer says no"  we dont except that here. :confused:
Sorry if this is the wrong place to ask, mods move it if it is.
You need to upload your photos to a place like Imgur and then press share and copy link to clipboard and finally post the link in your post here.
No he should be able to upload.
I used the windows 10 app to resize, but when uploading this site says it does not accept this format ? Not sure what format it needs to be?
I will keep playing around and eventually work it out. Not sure if the photos(file size) is too large or if it has to be Jpeg etc.