I am having the same problem that is described in a previous post (https://support.mozilla.org/en-US/questions/1106651). In that thread the original poster said that none of the suggestions worked and that he was moving to another email client. The problem is that Thunderbird is erroneously substituting graphics from a previous email. I just replied to an email that I received, and when I reviewed that email I saw that a graphic from an email a year ago had been substituted for the graphic in the email that I had sent. The previous graphic, which spanned the entire page, had been compressed down into the size of the graphic it replaced. This is not the first time. Two additional observations about the current error: i) both the previous email and the erroneous graphic email had the same email destination, and ii) there were eight unexplained copies in the draft folder (I may have saved it once, but not eight times). My guess is that in storage text and graphics are segregated, and that the index to the graphics is being corrupted.