I use my laptop to transfer photos onto the forum site from Flickr as I’ve had no joy from my mobile.
This is how I go about it
On Flickr:- (top black bar) go to cloud ‘upload’ option.
(Press blue bar) choose photo and video
Select file and photo (double click it)
If more than one photo, select add (top left)
For just one photo, select blue box top right of screen ‘upload’
In the ‘Photostream’ option double click the photo to share
Select ‘share photo’ (arrow bottom right)
Select size 480x640
Right click on the image file to highlight and then click to copy
Go to forum post, and on the page, right click. Select ‘paste’ option.
In forum ‘preview’ option edit out text upto ‘IMG’
...........and post
Note writing below this will create a link to Flickr
Good luck