To show a photo or image in a post or reply, open a New Topic or Reply window, click Attachments below left of the post window , then click Add files which will open your computer's file list, highlight a file (preferably in a .jpg, .jpeg, .bmp or .gif format), click Open at the bottom of the window, wait for it to upload and it should show the filename in the original post page, put the cursor in the post where you want the photo and click Place inline which will add the filename inside [ attachment] [ /attachment] code. You can Add files several times, max 4 per post. Then Submit the post. You don't need to use [ URL] [ /URL] or [ IMG] [ /IMG] tags .
This method relates to Windows computers, but the words may be different on Apple computers, iPads or iPhones.
If the upload shows a message that the image is too large, it may be size in pixels or file size in KiB (2 MB or 2000 KiB at 01/09/2020). Size in px is unlimited at but 800 x 600 px is quite sufficient for a website. Most computers have image software that can resize images and save with a .jpg or a .jpeg extension. Windows computers have "Paint" (search for mspaint.exe or paint.exe or Paint if you can't find the program).