DPI refers to "dots per inch", which is used to determine the resolution of an image when printed. The resolution of a raster digital image (such as a JPEG) is determined solely by the number of pixels it contains (horizontally and vertically), so the DPI of an image is not relevant (in terms of its resolution) unless it is printed.
If an image contains a DPI then this will simply be a numeric value stored in the image‘s header (as part of its embedded metadata). Software such as Photoshop may read this value and use it to determine the size at which the image is printed or displayed.
For example, if you have an asset that is 1000 pixels square and it has a DPI setting of 70 then if you print it using software that uses the DPI setting then it will be printed quite large, with not particularly good resolution on the printed page. If you then change the DPI setting to 300 and print it then it will be much smaller, but with better resolution. The resolution of the digital image itself remains unchanged.
Changing the DPI of a digital image does not increase its resolution. If you think about it, this makes sense - where would the extra information need to do this come from? (Actually, if you change the DPI in Photoshop without keeping the pixel size the same it does attempt to resample or interpolate upwards, but this usually results in a loss of detail and sharpness).
If users are interested in determining whether a digital image is high-res they should look at its pixel size, which they can find in the asset view sidebar in Dash.
How does Dash handle embedded DPI in assets?
Dash preserves all embedded metadata that's in the original file when it is uploaded, so if an asset contains a DPI value in its embedded metadata, this will still be there if you redownload the Original version of the asset.
When downloading a custom size, Dash strips out embedded metadata. This is primarily as part of optimising the file for web use, as removing metadata reduces the file size.
How does Photoshop determine an image's DPI setting?
If you open an image in Photoshop and go to Image->Size it will show a DPI setting. Photoshop uses the following embedded metadata fields to determine this:
ResolutionUnit (set to "inches").
If these values are missing from the image's metadata header then Photoshop defaults to showing the DPI as "72".
Therefore, because Dash strips out all embedded metadata, any converted (web ready) image you download from Dash will show as 72 DPI in Photoshop. As discussed above, this is completely irrelevant unless you intend to print the image (in which case you can usually adjust the DPI in the software you are using to print it).