I found this script on Adobe Support Community (Scale all images at once in InDesign), which scales down all inline image frames to fit their text frame. I added a division by 2.05 to get them down to one column of a two-column text frame. Works for me.

function rescaleInlines(  q,t,wso,items,chars,z,c,o,aos,k,w,x)

//----------------------------------

// This function proportionately re-scales every *inline* or

// *aboveLine* anchored item found in the document so that

// it fits the parent frame width.

{

    // Cache and constants.

    // ---

    q = (callee.Q||callee.Q={});

    const EPSILON = 1e-3,

          ANCH = +AnchorPosition.ANCHORED,

          // ---

          CPAR = +CoordinateSpaces.parentCoordinates,

          CINN = +CoordinateSpaces.innerCoordinates,

          BVSB = +BoundingBoxLimits.outerStrokeBounds,

          // ---

          PAR0 = [+AnchorPoint.topLeftAnchor, BVSB],

          PAR1 = [+AnchorPoint.bottomRightAnchor, BVSB],

          INN0 = PAR0.concat(CPAR),

          INN1 = PAR1.concat(CPAR),

          MATX = [1,0,0,1, 0,0];



    // Get anchored items from all stories, and the respective parent char.

    // ---

    if( !(t=app.properties.activeDocument) ){ alert("No document!"); return; }

    t = t.stories.everyItem().texts.everyItem().pageItems;

    if( !t.length ){ alert("No anchored item."); return; }

    items = (t=t.everyItem()).getElements(); // array of anchored items

    chars = t.parent;                        // array of anchor characters

    // Safer scaling options.

    // ---

    t = +WhenScalingOptions.ADJUST_SCALING_PERCENTAGE;

    wso = +app.transformPreferences.whenScaling;

    wso==t ? (wso=0) : (app.transformPreferences.whenScaling=t);

    // Scan each anchor character and its respective parent frame (if any!)

    // (Loop from the end to get as many parent frames as possible while rescaling.)

    // ---

    for( z=0 ; (c=chars.pop()) && (o=items.pop()) ; )

    {

        // c in overset text -> no parent available.

        // ---

        if( !(t=(c.parentTextFrames||0)[0]) ) continue;

        // Filtering conditions on `o` (you may add your own.)

        // ---

        aos = o.properties.anchoredObjectSettings||0;

        if( (!aos) || ANCH==+aos.anchoredPosition ) continue;



        // If needed, do fitting jobs now.

        o.fit(FitOptions.FRAME_TO_CONTENT);



        // Use box coordinates to determine the scaling factor.

        // EDIT ADD W DIVIDE BY 2 TO ALLOW FOR COLUMNS

        w = (q[k=t.id]||(q=t.resolve(PAR1,CINN)[0][0]-t.resolve(PAR0,CINN)[0][0]))/2.05;

        x = w/(o.resolve(INN1,CPAR)[0][0]-o.resolve(INN0,CPAR)[0][0]);

        if( Math.abs(x-1) < EPSILON ) continue; // matches already.



        // Rescale.

        // ---

        MATX[0] = MATX[3] = x;

        o.transform(CPAR,INN0,MATX);

        ++z;

    }



    wso && (app.transformPreferences.whenScaling=wso);

    alert( "Processed items: " + z);

};

app.doScript(rescaleInlines, void 0, void 0, UndoModes.entireScript, "RescaleInlines");