specify image dimensions for FC stories thumbnails

Hello,
Each time I check my site with GTmetrix, I get a bad note on the 'specify image dimensions' criteria, although I take great care to specify those dimensions for any image I put on my site.

But the problem is only coming from images like :
/images/stories/flexicontent/l_aides-financieres-r-volt-aerovoltaique-byo-o.png (Dimensions: 200 x 168)
/images/stories/flexicontent/l_domofinance-200x118.jpg (Dimensions: 200 x 118)
/images/stories/flexicontent/l_electroluminescence-panneau-photovoltaique.png (Dimensions: 400 x 230)
/images/stories/flexicontent/l_loubieres-foix-aerovoltaique-rvolt-systovi-recto-verso-800x900.jpg (Dimensions: 266 x 300)
/images/stories/flexicontent/l_photovoltaique-les-clefs-anti-arnaque-800x500.jpg (Dimensions: 400 x 250)

It is always a 5 images list, so I guess it comes from the Addthis recommended content widget that uses those thumbnails.
Do you know if there is a way to force FC to specify those image dimensions, or do you think it is only a addthis problem?

Thanks for your help.

Flo

Hello

yes it is prefered to have image dimensions, as this gives better user experience,

it avoids need for browser to repositioning / repaint the contents while page is loading,
effectively makes loading seem faster, and it is also more convenient for the user as text is not moved during page rendering

we need to update (check and update wherever missing) the image/gallery, checkboximage, radioimage etc fields
i will open a short-term issue e.g. v3.0.15 (adding this should not break anything)
github.com/FLEXIcontent/flexicontent-cck/issues/477

ok, thanks