How to scrape image URL from a webpage?

Just for fun, I scraped together some pretty abhorrent M using the GUI, pointed at a wikipedia article. Here's what it looks like if you scrape all images from https://en.wikipedia.org/wiki/The_Lord_of_the_Rings:_The_Return_of_the_King

After all the mangling and filtering, the M came out like this:

let
    Source = Table.FromColumns({Lines.FromBinary(Web.Contents("https://en.wikipedia.org/wiki/The_Lord_of_the_Rings:_The_Return_of_the_King"), null, null, 65001)}),
    #"Filtered Rows" = Table.SelectRows(Source, each Text.Contains([Column1], "src=""//upload")),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Filtered Rows", "Column1", Splitter.SplitTextByEachDelimiter({"src=""//"}, QuoteStyle.None, true), {"Column1.1", "Column1.2"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Column1.1", type text}, {"Column1.2", type text}}),
    #"Split Column by Delimiter1" = Table.SplitColumn(#"Changed Type", "Column1.2", Splitter.SplitTextByEachDelimiter({""""}, QuoteStyle.None, false), {"Column1.2.1", "Column1.2.2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Delimiter1",{{"Column1.2.1", type text}, {"Column1.2.2", type text}}),
    #"Removed Columns" = Table.RemoveColumns(#"Changed Type1",{"Column1.1", "Column1.2.2"}),
    #"Filtered Rows1" = Table.SelectRows(#"Removed Columns", each Text.EndsWith([Column1.2.1], ".jpg") or Text.EndsWith([Column1.2.1], ".png") or Text.EndsWith([Column1.2.1], ".gif")),
    #"Added Custom" = Table.AddColumn(#"Filtered Rows1", "https", each "https://"),
    #"Reordered Columns" = Table.ReorderColumns(#"Added Custom",{"https", "Column1.2.1"}),
    #"Merged Columns" = Table.CombineColumns(#"Reordered Columns",{"https", "Column1.2.1"},Combiner.CombineTextByDelimiter("", QuoteStyle.None),"Merged"),
    #"Renamed Columns" = Table.RenameColumns(#"Merged Columns",{{"Merged", "Images"}}),
    #"Duplicated Column" = Table.DuplicateColumn(#"Renamed Columns", "Images", "Images - Copy"),
    #"Renamed Columns1" = Table.RenameColumns(#"Duplicated Column",{{"Images - Copy", "ImageURLs"}})
in
    #"Renamed Columns1"

There's definitely a few things I could do here to clean it up, but the point is, you're going to have to load the webpage as a text file and start filtering down to context around the link you need. Once you isolate the links as full URLs, you can set the column type to "Image URL" and use those images in your Power BI report.