If you are getting an Alert (you don't say Avast is stopping you), it should have options, one being Exclude.
That said you are the one at risk of your actions.
A screenshot of may help us to helpAttaching Images to your post - When you Click the Reply button it opens a text window for you to post your comment (reply or post).
Click the Preview button, that shows what you have input and expands it to include 'Attachments and other options'. Click that it further expands, here you can attach images, etc. at the bottom of your post.
See my attached image, click to expand. you.
