I think this is an interesting question and I think I have a good solution so I will answer my own question.
Since this is a movie and I have many frames, I decided to loop through (most of) the frames and identify which pixel values differ between consecutive frames. This indicates movement and helps identify the "static" regions of the image, e.g. the top blue banner. By determining which pixels experience movement in the image throughout the analyzed frames, I can then compute a convex hull of those pixels. From there, a bounding box gives an approximate location of the region in question.
% imFolder = % The directory/folder holding all relevant im.
imFileName0 = [imFolder,'\050'];
N = dir([imFolder '/*.tif']); % # of images in folder.
nFrames = size(N,1);
interval = 5; % # of frames skipped.
viewFrames = 1:interval:nFrames-1;
viewFrames = [viewFrames,nFrames-1];
% Read first image frame, convert to binary.
[I0,~] = imread([imFileName0,'.tif']);
% Initialize a binary image for identifying pixels that capture movement.
pix = zeros(size(I0));
% Loop through until the N-th frame, creating all-encompassing mask.
findSlash = strfind(imFileName0,'\'); % Find last forward-slash.
findFrameNum = findSlash(end)+1:length(imFileName0);
for idx = viewFrames(1:end)
% Get next frame.
nextFrameNum = num2str(str2double(imFileName0(findFrameNum)) + idx);
if length(nextFrameNum) == 2
nextFrameNum = ['0',nextFrameNum]; %#ok<AGROW>
imFileNameNextFrame = imFileName0; % Filename of next frame.
imFileNameNextFrame(findFrameNum) = nextFrameNum;
INext = imread([imFileNameNextFrame,'.tif']); % Read next image frame.
% Compare (nonbinary) the previous frame with nextFrameNum.
dynamicPixels = INext ~= I0;
pix(dynamicPixels) = 1;
% I0 becomes INext because we are comparing consecutive frames.
I0 = INext;
% Compute convex hull of pix to bound all changing-pixels.
CH = bwconvhull(imbinarize(rgb2gray(pix),'adaptive','Sensitivity',1),'union');
% Identify coordinates of a bounding box encasing all binary values in CH.
%%%alphaShape % Might be beneficial to use.
bb = regionprops(CH,'boundingbox');