How important is the filename of an image?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  David Jones: How important is the filename of an image? I have hundreds of images in a site with random numbers for the filename, I have been editing the permalinks for these image pages so that they have the correct product name in, I know that using a descriptive title for each image is better for SEO and Google but if I do this for all my images its going to be a HUGE task as I will have to reattach them to post pages etc and a bunch of other stuff, is it really worth me doing this or should I just go with editing the permalinks?
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  Federico Sasso: In my experience it's more important if you depend a lot on Image Search; for normal Web Search might not be worth the effort, in presence of other stronger on-page signals.
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  Walid Al-Yousef: Alternativebl text is important if you cant control image filename
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  Richard Brus: The image title tag isn't as important as the image 'alt' tag for seo. If your missing your image alt tags then it's actually classed as invalid markup.
  
  If you want to persist and add title tags, which are still important, attack the job in a wise manner.
  
  Copy all of the page's code from the editor and paste it into notepad++. Then do a swap and replace. Just find all (" alt=")  ;and replace with (" title="" alt+")  ; Now you have an image tag on every picture of the page in under 5 seconds.
  
  Now just go through the code & put your cursor in between the title tag quotation marks ( title="*" ) and speak your title using your windows speech recognition or Dragon Naturally speaking. I could probable name about 50 images in 10 mins doing it this way.
  
  And the jury's still out on how important file names are for seo. The truth is that no one knows just how much weight the algorithm puts on this but I'd say it contributes to less than 2% of a pages overall on-page seo score.  ;
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  E.Dieter Martin: It's worth doing, at least from now on. You could also think about going back 2-3 months of posts and fix those as well, as Google likes fresh content, and the payoff becomes smaller with older posts. Next option to cut down the number of images to fix is to check the search rankings on Google webmaster tools and select the ones you'd like to see ranking better.
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  Daniel Olvera: Apply the 80/20 rule and attack it that way. Alt tags are part of usability and Gogle likes it when you put the extra effort. If haven't done it yet, edit your permalink structure on the settings so you don't have to enter them manually going forward.
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  Corey Willey: Others will say it is not an important task it WILL be quite important that at least the target keyword is included in the title. It already carries weight and as google expands its algorithm it only makes sense that they will expand the demands for pictures like they do content. Think about it this way its a 5 second task today or a week long task in the future. If you have a bunch of pictures theres probably a program that you can download that will change all titles
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  David Jones: Thanks for the answers. So I found a VERY helpful plugin called 'Media rename' which lets you rename all your images and their titles within wp without having to re-upload them. Ive already started renaming all the files and their titles so now each images permalink is exactly how I want it: Domain.com/product-name/image-name and of course all the images have been given basic but descriptive names now. The plugin allows you to do this from the media library level by just ticking a box next to each image, typing the new file and title name for each image in a field then hitting the 'Apply' button but if I want to add alt text then I need to go into each image individually and add it. Is this really necessary? Surely the descriptive permalink of the image location with the same filename for the image is enough for search engines to know what it is?
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  David Jones: ...also, can anyone recommend any plugin that allows me to quickly add/edit alt text to images in the media library? So far Ive only found 'SEO friendly images' but the reviews are mixed...
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  David Jones: ok well to answer my own question Im getting someone to make the alt text of all images the same as the image filename/title via a Mysql injection
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  W.E. Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:45:57 into the YouTube video: https://dumbseoquestions.com/q/how_important_is_the_filename_of_an_image