To post an image from your Dropbox account onto the TexAgs forums you'll need to obtain the image's shareable address. You can obtain that from:

(STEP 1 - Option A) The Dropbox website: Login at dropbox.com, and open the desired image.



Click the Share button to obtain the link, and copy it to your clipboard (Ctrl+C)



(STEP 1 - Option B) Your Computer: If you have Dropbox installed on your computer, open the Dropbox folder containing the image and right-click on the file. Select the option "Share Dropbox Link". This will copy the link to your clipboard.




Now that you have the shareable image address copied to your clipboard

(STEP 2) Post the image on TexAgs: Within your desired post, click the "insert image" icon in the toolbar and Paste (Ctrl+P) the link from your clipboard. IMPORTANT: You will need to change the end of the address to say "dl=1" instead of "dl=0".

The address should look something like: https://www.dropbox.com/s/randomcharacters/filename.jpg?dl=1

Result:

agreed. Dropbox, by default, is giving you a link that presents the image on their website. For example:

https://www.dropbox.com/s/vnddhr1bk3dwq94/40_clb6_84b%5B1%5D.jpg?dl=0

They probably do this to try to get non-dropbox-users to sign up with them.