Take image file in question.
Open in Paint, or image editing software of your choice. Save as .PNG (this can increase the file size, sometimes massively).
Open Pngyu (available from https://pngquant.org) and drag .PNG image into Pngyu UI
Once happy that conversion has been successful, the original file(s) can be deleted.
Upload resulting file to Google Photos.
Open photo and click ‘share’ icon then ‘create link’ Copy resulting URL
Head to https://ctrlq.org/google/photos. Paste copied URL into field and hit ‘Generate Code’ Copy generated ‘Direct Link (URL)’ code.
Paste resulting url into message board post, highlight and select the ‘insert image’ button (or manually add the [img] and [/img] tags as required.
As a general rule, the link will have a width figure already added. This can be adjusted to suit or, alternatively, the image can be adjusted to size prior to uploading.